John Gill Commentary Jeremiah 45:4

"Thus shalt thou say unto him, Thus saith Jehovah: Behold, that which I have built will I break down, and that which I have planted I will pluck up; and this in the whole land." — Jeremiah 45:4 (ASV)

Thus shall you say to him
This is spoken to Jeremiah, and is an order from the Lord to him, what he should say in his name to Baruch: the Lord says thus, behold, [that] which I have built I will break
down, and that which I have planted, I will pluck up ;
the Jewish nation, both as to church and state; which the Lord has built up as a spacious and beautiful house to dwell in, and has planted as a vineyard, and set it with pleasant plants; but now would demolish this building, and destroy this plantation.

even this whole land ;
not a few cities only, or only Jerusalem the metropolis, but the whole land of Judea; no part of it but what should be left desolate. So the Targum says, 'even the whole land of Israel, which is mine.'