Jamieson, Fausset and Brown on Jeremiah 11:15

15. my beloved--My elect people, Judea; this aggravates their ingratitude (Jr 12:7).

lewdness with many--(Eze 16:25). Rather, "that great (or, manifold) enormity"; literally, "the enormity, the manifold"; namely, their idolatry, which made their worship of God in the temple a mockery (compare Jr 7:10; Eze 23:39) [Henderson].

holy flesh--(Hag 2:12-14; Tit 1:15), namely, the sacrifices, which, through the guilt of the Jews, were no longer holy, that is, acceptable to God. The sacrifices on which they relied will, therefore, no longer protect them. Judah is represented as a priest's wife, who, by adultery, has forfeited her share in the flesh of the sacrifices, and yet boasts of her prerogative at the very same time [Horsley].

when thou doest evil--literally, "when thy evil" (is at hand). Piscator translates, "When thy calamity is at hand (according to God's threats), thou gloriest" (against God, instead of humbling thyself). English Version is best (compare Pr 2:14).