“Bethel…Gilgal.” The towns of Bethel and Gilgal were two centers of pagan worship in Israel. Jeroboam I, the first king of Israel, set up a golden calf in Bethel soon after Solomon died (1 Kings 12:28-29).
“and sin.” This is irony. The prophet is magnifying the sin by making an ironic statement about it. He is certainly not encouraging the people to go sin by worshipping idols. The same kind of irony is used by Isaiah (Isa. 50:11).