Jamieson, Fausset and Brown on Jeremiah 6:15

15. Rosenmuller translates, "They ought to have been ashamed, because ... but," &c.; the Hebrew verb often expressing, not the action, but the duty to perform it (Ge 20:9; Mal 2:7). Maurer translates, "They shall be put to shame, for they commit abomination; nay (the prophet correcting himself), there is no shame in them" (Jr 3:3; 8:12; Eze 3:7; Zep 3:5).

them that fall--They shall fall with the rest of their people who are doomed to fall, that is, I will now cease from words; I will execute vengeance [Calvin].