Jeremiah expresses his confusion as he compares himself to a gentle lamb led to the slaughter.
The emphasis seems to be on the fact that, just like a lamb does not know what is happening when taken to be slaughtered, so Jeremiah did not know what was happening to him. I did not know it was against me they devised schemes.
19 But I was like a gentle lamb led to the slaughter. I did not know it was against me they devised schemes, saying, “Let us destroy the tree with its fruit, let us cut him off from the land of the living, that his name be remembered no more.”