“8:8 Literally translated, ‘The lying pen of the scribes has made it into a lie.” Scribes (sometimes translated “secretaries”) were not responsible to interpret or teach the law until postexilic times (Ezra 7:11). In Jeremiah’s day, scribes primarily wrote and transcribed documents (Jeremiah 36:32). Teaching was the work of priests (Deuteronomy 33:10) and was done orally. Therefore, this verse could be understood to mean that the scribes had purposefully made inaccurate copies of the scrolls containing God’s law. Because the people were taught from these corrupted scrolls, they believed lies rather than truth.”
Bright, B. (2007). The Discover God Study Bible NLT. Illinois: Tyndale House Publishers.

“Yet some biblical authors were aware that scribes could alter biblical texts for improper motives. In Jeremiah 8:8, we find this fascinating complaint: “How can you say, ‘We are wise, and the law of the LORD is with us…”

Avalos, H. (2007). The End of Biblical Studies. Michigan: Prometheus Books. p. 67

“In Jer. 88f. the prophet asks:How is it that you say, ‘Wise are we, and torah of Yahweh is with us’? yet, behold, into falsehood has the false pen of the scribes turn it into. Wise men will be shamed, shattered, and taken; behold, they reject the word of Yahweh, and what wisdom is there in them?”

The prophet’s hearers, then, are claiming to be wise and to possess the torah of Yahweh; the prophet protests that this torah has been corrupted by the scribes, and prophesies that those who call themselves wise will be destroyed, since they are in fact rejecting the divine word, and their wisdom is therefore unreal.”

Weeks, S. (1994). Early Israelite Wisdom: Oxford Theological Monographs. New York: Oxford University Press. pp. 85-86