Fourth Woe - against those who confound the distinctions of right and wrong (compare Rom 1:28), “reprobate,” Greek, “undiscriminating: the moral perception darkened.”
bitter ... sweet - sin is bitter (Jer 2:19; Jer 4:18; Act 8:23; Heb 12:15); though it seem sweet for a time (Pro 9:17, Pro 9:18). Religion is sweet (Psa 119:103).