Albert Barnes Commentary Jeremiah 8:4

"Moreover thou shalt say unto them, Thus saith Jehovah: Shall men fall, and not rise up again? Shall one turn away, and not return?" — Jeremiah 8:4 (ASV)

The prophet here resumes from (Jeremiah 7:28) the main subject of his prophecy. He again invites the Jews to repentance.

Shall they fall? – The argument is that when men fall, they do not lie upon the ground, but endeavor to get up again; and when a man loses his way, he does not persist in going on, but turns round, and retraces his steps. Israel then will be only following the dictates of common sense in desisting from that which she now knows to be her ruin.