John Gill Commentary Jeremiah 23:38

"But if ye say, The burden of Jehovah; therefore thus saith Jehovah: Because ye say this word, The burden of Jehovah, and I have sent unto you, saying, Ye shall not say, The burden of Jehovah;" — Jeremiah 23:38 (ASV)

But since you say, the burden of the Lord Seeing, notwithstanding all prohibitions of it, and directions to the contrary, they still persisted to call prophecy by this name, and that in a jocose and bantering way, and asked for it, and what it was, in a scoffing manner:

therefore thus says the Lord, because you say this word, the burdenof the Lord; will continue to use it, though so displeasing to me:

and I have sent unto you, saying, you shall not say, the burden of theLord; and therefore could not plead ignorance of his will, or excuse themselves, by saying they would have avoided it, had they known it was disagreeable to him: this was an aggravation of their impiety, that they should obstinately persist in it, after he had remonstrated against it by his messages to them.