We have come to the final chapter of Amos, and to the seer’s final vision, this time of the Lord and the altar.
As in previous passages in Amos, the altar in question is not the altar in Jerusalem, in the true temple of the Lord, but rather the altar of the facsimile-temple in Bethel, home of one of King Jeroboam I’s two golden calves, variously referred to as “the guilt of Samaria” and, more often, “the sins of Jeroboam the son of Nebat, which he made Israel to sin.”
That last bit is important. Jeroboam “made Israel to sin”.