Adam Clarke on Jeremiah 31:34

And they shall teach no more - It shall be a time of universal light and knowledge; all shall know God in Christ, from the least to the greatest; the children shall be taught to read the New Covenant, and to understand the terms of their salvation.

I will forgive their iniquity - It shall be a time of General Pardon; multitudes shall be daily in the Christian Church receiving the witness of God's Spirit, and in their life and conversation witnessing a good confession. How wonderfully is this prophecy fulfilled in the age of Bibles, Sunday schools, and village preaching.