Introduction:
The letter to the Colossians is sometimes taken to be the earliest surviving Pauline pseudepigraphon, and thus the earliest Christian forgery of any kind. But there is obviously no way to say for certain: we do not know who wrote the letter, to whom, or where. As a result, it is virtually impossible to establish its relative chronology in relation, say, to 2 Thessalonians. It is also difficult—again, well nigh impossible—to identify with any level of certainty the adversaries who are being opposed, although I will argue below that they are probably to be taken as real, not imaginary. What is most clear is that the author of the book is using Paul’s authority to attack them. Moreover, in doing so, the author has been more or less compelled, given the nature of the false teaching, to embrace eschatological views that stand at odds with Paul’s. As we will see, eschatology is not a peripheral issue in the letter. It constitutes one of its central features.

Views on Authorship

In 1838, Ernst Mayerhoff was the first to question the Pauline authorship of Colossians. In his view, the language and style of the letter were not sufficiently Pauline, certain terms were used in non-Pauline ways, the author attacked a heresy not found until after Paul’s day, and the book derived much of its teaching from Ephesians. Many of these issues have remained important parts of the conversation still today. In 1857, Heinrich Ewald was the first to argue that the differences from the Pauline letters were because the letter was penned by a Pauline associate, Timothy, a view that continues to have representatives among those who see the letter as basically Pauline but distinctive in greater or lesser ways.

Evidence of Forgery

1. As with every instance of forgery, the case of Colossians is cumulative, involving multiple factors. None has proved more decisive over the past thirty years than the question of writing style. The case was made most effectively in 1973 by Walter Bujard, in a study both exhaustive and exhausting, widely thought to be unanswerable.

Bujard compares the writing style of Colossians to the other Pauline letters, focusing especially on those of comparable length (Galatians, Philippians, and 1 Thessalonians), and looking at an inordinately wide range of stylistic features: the use of conjunctions (of all kinds), infinitives, participles, relative clauses, repetitions of words and word groups, use of antithetical statements, parallel constructions, use of the preposition, the piling up of genitives, and on and on. In case after case, Colossians stands apart from Paul’s letters. Here I can mention a slim selection of his findings. How often does the book of Paul use adversative conjunctions? Galatians 84 times; Philippians 52; 1 Thessalonians 29; but Colossians only 9. Causal conjunctions? Galatians 45 times; Philippians 20; 1 Thessalonians 31; but Colossians only 9. Consecutive conjunctions? Galatians 16 times; Philippians 10; 1 Thessalonians 12; but Colossians only 6. How often does the letter use a meeting to introduce a statement ( etc.)? Galatians 20 times; Philippians 19; 1 Thessalonians 11; but Colossians only 3. As a Fazit to part one, Bujard adds up conjunctions of all kinds and indicates the percentage of their occurrence in relation to all words used: Galatians 239 (10.7 percent), Philippians 138 (8.5 percent), 1 Thessalonians 126 (8.5 percent), Philemon 28 (8.4 percent), but Colossians only 63 (4 percent). The average in all the undisputed letters is 10.4 percent; in Colossians, it is 4 percent. Bujard then uses another metric, adding up all the conjunctions used in the Pauline letters: Galatians 33; Philippians 31; 1 Thessalonians 31; but Colossians only 21.

But he goes further, subtracting from these totals the conjunctions that occur in all the letters in question (the shorter epistles: Galatians, Philippians, 1 Thessalonians, 2 Thessalonians, Philemon, Colossians, and Ephesians), since these are simply common words, not words necessarily distinctive of Paul. One is then left with the following numbers: Galatians 24; Philippians 22; 1 Thessalonians 22; but Colossians only 12. He then goes a step farther, subtracting those that occur in all but one of the letters in question (these are distinctive of Paul, not just common words). And the results remain consistent, if not more graphic: Galatians 20; Philippians 18; 1 Thessalonians 18; but Colossians only 8.

The same (or rather the inverse) results obtain with reference to the use of relative clauses. In Romans they make up 1.4 percent of all the words of the book, 1 Corinthians 0.9 percent, 2 Corinthians 1.0 percent, Galatians 1.5 percent, Philippians 1.5 percent, 1 Thessalonians 0.3 percent, Philemon 1.4 percent, but Colossians 2.6 percent. Bujard goes on like this for a very long time, page after page, statistic after statistic. What is striking is that all these features point the same way. When one adds to these the other commonly noted (though related) features of the style of Colossians—the long complex sentences, the piling up of genitives, the sequences of similar sounding words, and so on—the conclusion can scarcely be denied. This book is not written in Paul’s style. Arguments based on style are strongly supported by considerations of content. In several striking and significant ways the teaching of Colossians differs from the undisputed letters. Most commonly noted is the eschatological view, to which we will return later in our discussion. In 1:13 the author insists that God (already) “has delivered us from the authority of darkness and transferred us into the kingdom of his beloved son.” Already? An aorist tense? Is this Paul? More striking still is 2:12–13, and 3:1, which insist that believers have already experienced a kind of spiritual resurrection after having died with Christ: “you were also raised [aorist] in him through faith”; God “made you alive with him”; “if then you have been raised up with Christ”—statements in clear tension with Paul’s emphatic statements elsewhere, such as Rom. 6:1–6, where it is quite clear that, whereas those who have been baptized “have died” with Christ, they decidedly have not been “raised up” with him yet. This is an important point in Paul’s theology, not a subsidiary matter. The resurrection is something future, something that is yet to happen. So too Phil. 3:11—“if somehow I might obtain to the resurrection from the dead.” And yet more emphatically in 1 Cor. 15—“in Christ all shall be made alive … we shall all be changed … the dead will be raised.” It can easily be argued that this is a key —if not the single key—to understanding Paul’s opposition to the Corinthian enthusiasts. They believed they were leading some kind of spiritual, resurrected existence, and Paul insisted that it had not yet happened. They may have died with Christ, but they had not yet been raised with him. That will come only at the end.

There are other theological differences from Paul, frequently noted, all of them pointing in the same direction. A later author has taken up Pauline themes and shifted them in decidedly non-Pauline ways. Unlike Paul, this author understands redemption as the “forgiveness of sins” (1:14; as does Eph. 1:7). The phrase occurs nowhere else in the Pauline corpus; indeed, the term itself, in the sense of “forgive sins,” is absent from Paul, except in the quotation of Ps. 32:1 in Rom. 4:7 (“Blessed are those whose lawless deeds are forgiven”). So too, analogously, with a different term, 2:13 speaks of trespasses being forgiven: is never used this way in the undisputed Paulines. So too 3:13 speaks of “forgiving one another just as the Lord has forgiven you,” using again.

This is far closer to the Johannine prologue than Paul. As a result, in comparison with Paul, the author of Colossians seems to have a much higher view of Christ (1:15–20) and a much lower view of the efficacy of his death (1:24).
Other differences from Paul may not be as striking but bear noting as contributing to the overall sense of the letter. It seems very odd indeed to have “Paul” attack issues of Jewish legalism (sabbaths and festivals 2:16; “regulations” involving purity and kosher 2:20–21) without using Pauline vocabulary either to describe or attack it (“law,” “commandment,” “justification”).

Given Paul’s ability to mix metaphor otherwise, possibly not too much weight should be placed on the fact that Christ here is described as the “head of the body” rather than the “body” itself (1:18), though the usage does give one pause. When one considers, however, how Paul imagines the life “of the body” the differences are even more striking. The Haustafel of 3:18–4:1 has long been thought of as non-Pauline, and for reasons related to the realized eschatology already noted. In particular, this domestication of Paul in his embrace of family ideals stands at odds with Paul’s firmly stated preference, for himself and others, for celibacy. Nowhere in Paul’s letters do we find such a celebration of standard Greco-Roman ethics; on the contrary, Paul insisted on the superiority of the ascetic life free from marriage (1 Corinthians 7). This, indeed, was the appropriate response to a world that was in the process of “passing away.” Here in Colossians, on the other hand, the world is not passing away (there is no imminent crisis); it is here for the long haul, and so are the Christians who make up Christ’s body in it. As a result, they need to adopt behavior appropriate for the long run. Relations to those living outside the community are especially important, not to inform them of the “impending crisis” but to maintain a proper upstanding relationship. In short, this is written by someone who knows the church has been here and will be here for the long run. There is no imminent expectation of the coming end. On the basis of all these considerations, it is clear that with Colossians we are not dealing with a letter of Paul, but a letter of someone wanting his readers to think he is Paul.

As Standhartinger indicates, the specific address to Colossians in fact seems at odds with the universal tendency of the letter (1:6, 1:23, 1:28, 2:1, 4:16). As a result, she may be right that the letter was (pseudonymously) directed there for symbolic value. Colossae was a remote, little known place; this embrace of the fullness of the divinity in bodily form reaches into the very remote corners of the empire.

2. Another argument against ‘Colossians’ is With regard to the Christian community envisioned by the radical Paul, those texts are contradictory, conservative, and regressive. They are not just post-Pauline; they are anti-Pauline. With regard to the norms of Roman society, they might even be too liberal. First of all, they advocate reciprocal duties for slaves owners—even granted that four-to-one ratio. Second, Paul directly addresses slaves as well as owners, and Roman slave owners would never accept that interference with their property.

In Raymond E. Brown’s Introduction to the New Testament he cites multiple studies of hundreds of scholars and says that about 80% of critical scholarship believes Ephesians is pseudonymous, while around 60% of critical scholarship believes Colossians is pseudonymous. Now his book was published in 1997, so these numbers may have changed, but likely not too much.
The arguments for Colossians that Brown presents are:

1. Colossians has a slightly different style than the more authentic Pauline letters. It’s sentences tend to be much longer than Paul usually writes, and it’s been described as a particularly “liturgical hymnic style”. Brown mentions the idea that this could be due to a scribe (Timothy is named as a co-sender of the epistle in its introduction after all). Perhaps he shaped its style more? However, Brown also brings up that most scholars reject this, since the different style is still heavily present in key-arguments, meaning it’s about as unlikely that Paul dictated it as it is that he just wrote it himself.
2. Colossians presents a slightly different theology. An example of this would be a heightened emphasis on “creation through Christ and his preeminence” that’s absent from the more authentic Pauline letters. Brown mentions that this may be emphasized in order to deal with the specific “false teaching” that Colossians addresses (which Brown further addresses as either Gnosticism, syncretism, or mystery religion). Brown further addresses that some scholars would date the appearance of these groups later into Christian history, after Paul’s death (and even into the second century), but also states that those datings are, in large part, guess work and estimations. Another difference in theology is that Colossians tends to demonstrate a more “realized eschatology” as opposed to the “future eschatology” that Paul often seems to hold. However, again, Brown refutes this by saying Colossians’ realized eschatology is often overstated, and points to verses like Col 3:4 to show that the author of Colossians did have some kind of future eschatology.
3. It presents a more developed ecclesiology. In many of the more authentic Pauline letters, the focus is on individual churches while in Colossians, we see for the first time the idea of a more universal Church, it’s role in the “heavenly powers”, and how this broader Church is the body of Christ. Brown does address however, that Colossians, if authentic, would be one of Paul’s later letters chronologically. He then leaves it a bit open ended on whether the ecclesiology could have developed to that point within Paul’s lifetime.
   With all of this, Brown says the evidence “favor[s], but not conclusively, an author other than Paul”, which seems to be fairly representative of the 60% previously discussed. As for Ephesians, it suffers from much the same problems. So why do less scholars favor it? Well, it shares the same problems because (like you said) it likely copies extensively from Colossians. Of the 155 verses of Ephesians, between one third to one half directly parallel Colossians in both order and content, and one third of the words found in Colossians are also found in Ephesians. This is unprecedented among Paul’s authentic letters. Further, it amplifies some of the previous problems that Colossians had, with Brown saying that “the florid style is like that of Col but even more expansive and hyperbolic (e.g., almost fifty uses of “all”), producing sentences of remarkable length… There are piled up adjectives and genitives, and redundant style and terms quite uncharacteristic of the Pauline usage in the undisputed letters.”

The author of Colossians

If he came from Paul’s school, he was a terrible student, or an extremely disloyal one.
“A close examination suggests that Colossians is inauthentic to Paul on several counts. While its author knows Paul’s distinctive theological vocabulary (e.g. “principalities and powers,” “love” [agape], “justification,” “body of Christ”), he puts this vocabulary in service to a Christology and eschatology* distinct from that of Paul’s authentic letters. The authentic epistles* speak of “justifica-tion” and “sanctification” in the present (see Rom 6.4–5) but reserve “salvation” for the future; for Colossians, salvation is a present reality (3.1–4), and justification has no place at all. A stronger argument against the authenticity of Colossians lies in its inclusion (3.22–4.1)—the earliest in the New Testament—of the hierarchical description of household relations called, since Martin Luther, “Haustafeln,” or “household codes.” In his authentic letters, Paul’s description of marital relation-ships is remarkably nonhierarchical (cf. 1 Cor 7.1–4, where husbands and wives each serve the oth-er); he was an antagonist to the kind of marital hierarchy promulgated in the household codes* of both Deutero-Pauline letters, the pastoral letters 1 Tim and Titus, and 1 Peter, all products of the second or third generation of New Testament writers (cf. Eph 6.5-9; Tit 2.1ff; 1 Tim 2.8ff and 6.1-2; 1 Pet 2.18-21.) These post-Pauline authors were aware that the parousia* of Jesus was not likely to occur in the near future, and felt they needed to provide guidelines on how his followers should live. Colossians also shares multiple phrases with Ephesians, another Deutero-Pauline letter (see “Colos-sians and Ephesians: Parallels,” p. ???). While Paul was not unconcerned with the behaviour of his the members of his churches in families, in worship, and in society, he urged flexibility, not rigidity.
If Paul did write the letter, he wrote under circumstances that forced him to adopt theological and social ideas strongly at variance with those we find in letters we know to be authentic.”

1. 
   Oxford Annotated Bible, page 1707, Michael David Coogan, Marc Zvi Brettler, Carol Ann Newsom, Pheme Perkins: Colossians lacks some central Pauline terms (e.g., righteousness, justification), uses new theological vocabulary (e.g., to be raised with Christ), and is composed in a more elevated, liturgical style. Colossians presents a vision of believers’ present lives as almost completely transformed by Christ’s death and resurrection (3.1–4), a contrast to Paul’s characteristic tension between the partial experience of God’s blessings in the present in light of the future resurrection (e.g., Rom 6.4; 1 Cor 15.50–58). Colossians also uses the Greco-Roman format of household rules to define ethical norms (3.18–4.1), which is more characteristic of the post-Pauline Ephesians, Pastoral Letters, and 1 Peter. Paul’s own ethical instructions did not reinforce or even focus on these household relationships; Paul instead adopted a baptismal creed that overturns social, ethnic, and gender hierarchies (Gal 3.28), and elevated celibacy over marriage (e.g., 1 Cor 7).