Emil Schürer writes (The Literature of the Jewish People in the Time of Jesus, pp. 329-331):

While this shorter explanation in a catechetical form [Questions and Answers on Genesis] was intended for more extensive circles, Philo’s special and chief scientific work is his large allegorical commentary on Genesis, Νομων ιερων αλληγοριαι (such is the title given it in Euseb. Hist. eccl. ii. 18. 1, and Photius, Bibliotheca cod. 103. Comp. also Origen, Comment. in Matth. vol. xvii. c. 17; contra Celsum, iv. 51). These two works frequently approximate each other as to their contents. For in the Quaestiones et solutiones also, the deeper allegorical significance is given as well as the literal meaning. In the great allegorical commentary on the contrary, the allegorical interpretation exclusively prevails. The deeper allegorical sense of the sacred letter is settled in extensive and prolix discussion, which by reason of the copious adducting of parallel passages often seems to wander from the text. Thus the entire exegetic method, with its draggin in of the most heterogeneous passages in elucidation of the idea supposed to exist in the text, forcibly recalls the method of Rabbinical Midrash. This allegorical interpretation however has with all its arbitrariness, its rules and laws, the allegorical meaning as once settled for certain persons, objects and events being afterwards adhered to with tolerable consistency. Especially is it a fundamental thought, from which the exposition is everywhere deduced, that the history of mankind as related in Genesis is in reality nothing else than a system of psychology and ethic. The different individuals, who here make their appearance, denote the different states of soul (τροποι της ψυχης) which occur among men. To analyse these in their variety and their relations both to each other and to the Deity and the world of sense, and thence to deduce moral doctrines, is the special aim of this great allegorical commentary. Thus we perceive at the same time, that Philo’s chief interest is not—as might from the whole plan of his system be supposed—speculative theology for its own sake, but on the contrary psychology and ethic. To judge from his ultimate purpose he is not a speculative theologian, but a psychologist and moralist (comp. note 183).

The commentary at first follows the text of Genesis verse by verse. Afterwards single sections are selected, and some of them so fully treated, as to grow into regular monographs. Thus e.g. Philo takes occasion from the history of Noah to write two books on drunkenness (περι μεθης), which he does with such thoroughness, that a collection of the opinions of other philosophers on this subject filled the first of these lost books (Mangey, i. 357).

The work, as we have it, begins at Gen. ii. 1; Και ετελεσθησαν οι ουρανοι και η γη. The creation of the world is therefore not treated of. For the composition, De opificio mundi, which precedes it in our editions, is a work of an entirely different character, being no allegorical commentary on the history of the creation, but a statement of that history itself. Nor does the first book of the Legum allegoriae by any means join on to the work De opificio mundi; for the former begins at Gen. ii. 1, while in De opif. mundi, the creation of man also, according to Gen. ii, is already dealt with. Hence—as Gfrörer rightly asserts in answer to Dähne—the allegorical commentary cannot be combined with De opif. mundi as though the two were but parts of the same work. At most may the question be raised, whether Philo did not also write an allegorical commentary on Gen. i. This is however improbable. For the allegorical commentary proposes to treat of the history of mankind, and this does not begin till Gen. ii. 1. Nor need the abrupt commencement of Leg. alleg. i seem strange, since this manner of starting at once with the text to be expounded, quite corresponds with the method of Rabbinical Midrash. The later books too of Philo’s own commentary begin in fact in the same abrupt manner. In our manuscripts and editions only the first books bear the title belonging to the whole work, Νομων ιερων αλληγοριαι. All the later books have special titles, a circumstance which gives the appearance of their being independent works. In truth however all that is contained in Mangey’s first vol.—viz. the works which here follow—belongs to the book in question (with the sole exception of De opificio mundi).

Emil Schürer comments:
“Περι συγχυσεως διαλεκτων. De confusione linguarum (Mangey, i. 404-435). On Gen. xi. 1-9.—The same title also in Euseb. H. E. ii. 18. 2. In the Praep. evang. xi. 15, Eusebius quotes several passages from it with the mistaken statement, that they are from: Περι του το χειρον τω κρειττονι φιλειν επιτιθεσθαι.” (The Literature of the Jewish People in the Time of Jesus, p. 335)

J. H. A. Hart writes (The Jewish Quarterly Review Original Series 17, pp. 118-122):

The de Confusione Linguarum opens thus: “As far as these things are concerned what has been said will suffice”—probably referring to the group of homilies relating to Noah—”next we must consider, and not casually (ου παρεργως), the philosophy of the narrative of the confusion of languages” (Gen. xi. 1-9). And now Philo explains the position of the antagonists, hinted at in the beginning of the de Gigantibus. Certain Jews, presumably Hellenists, disgusted with the ancestral polity, always grumbling and capping at the laws, use this and other such passages as stepping-stones for their atheism, impious that they are. They say “Do you still make solemn professions about your code as containing the canons of truth itself? See, your holy books contain myths such as you deride, when you hear others reciting them.” Well, we have not their leisure to search out these scattered myths, and will be content to deal with the passage in hand.

The first parable is the myth of the Aloeidae, who piled Ossa upon Olympus and Pelion upon Ossa. But notice Moses speak of a tower. The second is a myth, akin to that before us, relating to the common speech of living things recorded by fabricators of myths. It is said that in ancient times all living things, animals, fishes, and birds, had a common speech, so that they could sympathize with each other’s sorrows and joys, as now Greek with Greek and barbarian with barbarian. Then, sated with their unstinted supply of blessings, as often happens, they all turned to longing for the unattainable and treated for immortality, asking for destruction of old age and for perpetual youth, alleging that one of their number, the serpent, had already obtained this gift. But they paid the fitting penalty for their presumption; for their one common language was immediately cut up into different languages, so that they could not understand one another. Here again a discrepancy is to be noted, for Moses speaks only of men as having the same speech. It is said that the scriptural account is as mythical as the parables cited, and that the division or confusion of tongues was a cure for sins, intended to prevent men from conspiring together to do evil. But the latter theory is untenable. If wicked men wish to conspire they will not be stopped by the difference of their languages. They can always communicate, like men whose tongues have been cut out, by means of signs. Again, if a man learn many languages, he is always held in good repute among those who understand them, and regarded at once as a friend. In fact, the literal interpreters of the Law alone will refute these students of comparative mythology, without opposing sophistry to sophistry.

Well then, we understand this scripture to refer to the universality of evil both in the world and in the individual. Heaviest of all evils, and wellnigh incurable, is the cooperation of all parts of the soul in sin, when no one part is able to heal the rest, but physicians and patients are sick together, as at the time of the Deluge (Gen. iv. 5-7). We must flee all associations for purposes of sin, and confirm our agreement with companions of understanding and knowledge.

In this connexion the saying, “we are all sons of one man, we are peaceable” (Gen. xlii. 11), is introduced as an example of perfect harmony, and leads to a consideration of its origin and its complement. Inevitably will they love peace and hate war whose one and the same father is not mortal but immortal, God’s man, who being the Logos of the Eternal is of necessity himself also incorruptible. Their life is peaceful, while the polytheist’s is full of strife, and yet not, as some think, lazy and ignoble. Men of peace are men of war when opposed to the enemies of the soul’s peace. Such is the disposition of each lover of virtue, and the words of the inspired prophet bear the same testimony: “O mother, what manner of child am I? a man of war” (Jer. xv. 10).

“The East,” or “Dawn” (Gen. xi. 2), bears two meanings in Scripture, according as it refers to the dawning of light or of shadow in the soul. It is used in the good sense in the account of Paradise (Gen. ii. 8). So in the oracle of one of Moses’ companions (Zech. vi. 12), “Behold a man whose name is Dawn or ‘Rising’.” A most novel title this, if you suppose that a man composed of body and soul is spoken of; but if it be that bodiless man who is identical with the divine image you will confess that the title is most happy (ευθυβολωτατον). For him hath the Father of the universe raised up to be his oldest or first-begotten Son. “East” occurs in a bad sense in the story of Balak the fool and Balaam (Num. xxiii. 76 f.).

It is notable that these fools “find” the place most fitted for their folly, and “settle” there. Both points are significant. No wicked man is content with the crimes towards which his evil nature proceeds of itself, but invents fresh ones and therein abides. Therefore are all they whom Moses reckons wise introduced as sojourners, who reckon heaven their fatherland. Thence were they sent as colonists and thither they yearn to return (Gen. xxvi. 2, xxxiii. 4, xlvii. 9; Exod. ii. 22).

The mention of “bricks” (Gen. xi. 3) naturally suggests the bondage of Israel, in which the Egyptians compelled them to make bricks and to build fenced cities. The eye of the soul which alone can see God, bound in the bodily nets of Egypt, groans over its task (Exod. i. 11, ii. 23). But the way to freedom is sure. For all men labouring for gain, or fame, or pleasure there is ransom and salvation in the worship of him who alone is wise (Exod. viii. 1). Right is it for them that keep company with knowledge to aspire to see the Absolute and, if that they cannot, then at least his likeness, the most holy Word, and after him the world, the most perfect of sensible things; for philosophy is nothing else than to study to see these distinctly.

The Lawgiver uses “city” not only in the ordinary sense but also of that which a man carries about, built in his own soul, whereof those built on earth of material substances are but copies. How evil their city is, how shameless the exposure of their guilt, is shown by the warning of their conscience which foresees their impending dispersion (Gen. xi. 4). Their tower is like that recorded in the Book of Judgments, Phanuel, that is, “Aversion of God” (Judg. viii. 9).

The statement that “the Lord came down to see the city and the tower” (Gen. xi. 5) must certainly be understood metaphorically. To suppose that the Divine should really share the positions and motions of men is monstrous impiety (υπερωκεανιος και μετακοσμιος ως επος ειπειν ασεβεια). The human phrases are applied to God, who is not human in form, for the benefit of our education. And this particular expression is by way of being an exhortation, that no one should refrain from examining things closely, or judge by hearsay (Exod. xxiii. 1). Let no one think that the addition “which the sons of men had built” is otiose and insignificant. We must track out the hidden treasure of Scripture. The “sons of men” are polytheists; the worshippers of the One are styled “sons of God” (Deut. xiv. i, &c.).

The words put in God’s mouth need careful attention, “Come and let us go down and confound there their tongue” (Gen. xi. 7). For he appears to be speaking to some who are as it were his fellow workers, as at the creation of man (Gen. i. 26, cf. iii. 22). First, it must be said that there is no existing being equal in dignity with God: there is one Ruler and Governor and King, to whom alone it belongs of right to govern and order the universe. The poet’s saying, “the rule of many lords is no good thing; let there be one lord, one king,” applies better to the world and God than to cities and men. The next point is that God, being One, has innumerable Powers around him, all defenders and saviours of the universe, and with them the Powers of punishment, that is the prevention and correction of sins. By these the ideal world was framed and man also. God entrusts to them tasks which befit him not, for man is prone to err in his free choice between good and evil, and the way toward evil in the rational soul must not be created by God through himself. So God is the cause of all good and of no evil at all; the evil is allotted to his angels or Powers, which work under his supervision.

God says, “let us confound their tongue.” It is not, then, as the literalists suppose, simply the division of the speech of mankind which is the penalty of their sin. Yet I would not blame those who follow the superficial sense, for perhaps even they have reached the truth; but I would urge them not to be content therewith, but to come over to the metaphorical interpretations, regarding the letter as the shadow and the inherent spirit as the fact or substance. By choice of the word confusion the Lawgiver directly suggests a deeper meaning. If he referred only to the origin of different languages, distinction would have been the better word. Confusion is the abolition of the powers of each element of a compound or mixture in order to the production of the compound. Here the end in view is the dissolution of the fellowship of wickedness. And if we apply the Scripture again to the individual, it is obvious that God has separated the parts of the soul. It is fitting for God to tune the harmony of the virtues and to dissolve and destroy that of the vices. Now confusion is the most appropriate name of wickedness, as any fool proves plainly, as his words, counsels, and actions are all reprobate and confusion.