Albert Barnes Commentary Jeremiah 7:28

"And thou shalt say unto them, This is the nation that hath not hearkened to the voice of Jehovah their God, nor received instruction: truth is perished, and is cut off from their mouth." — Jeremiah 7:28 (ASV)

A nation - The “nation.” Israel holds so unique a position among all nations that for it to disobey God is marvelous.

Truth ... - Fidelity to God. Though they have the name of Yahweh often upon their lips and swear by Him (Jeremiah 5:2), yet it is only profession without practice.