John Gill Commentary Jeremiah 26:4

"And thou shalt say unto them, Thus saith Jehovah: If ye will not hearken to me, to walk in my law, which I have set before you," — Jeremiah 26:4 (ASV)

And you shall say to them
What follows is the substance of the prophecy, and the sum of the sermon or discourse he was sent to deliver, without diminishing a word of it: thus says the Lord, if you will not listen to me, to walk in my law
which I have set before you ;

first by Moses, by whose hands it was given to their fathers; and by the prophets, the interpreters of it to them; before whom it was set as a way for them to walk in, and a rule to walk by; a directory for them in their lives and conversations; and which continues to be so, as it is set before us Christians by our King and Lawgiver Jesus Christ; though not to obtain righteousness and life by the works of it; which should not be sought for, nor are attainable thereby.