Walk through Amos, verse by verse, with the great Bible Commentaries of Matthew Henry (1662 - 1714) & Adam Clarke (1760 - 1832)
3:14
That in the day that I shall visit the transgressions of Israel upon him I will also visit the altars of Bethel: and the horns of the altar shall be cut off, and fall to the ground. KJV
{For in the day, when I shall begin to visit the trespassings of Israel on him, I shall visit also on the
altars of Bethel; and the horns of the altar shall be cut away, and shall fall down into the earth.} Wycliffe's Bible
In the day that I shall visit - When Josiah made a reformation in the land he destroyed idolatry, pulled down the temples and altars that had been consecrated to idol worship, and even burnt the bones of the priests of Baal and the golden calves upon their own altars.
Note, If men will not destroy idolatrous altars, God will, and those with them that had them in veneration. Some make the horns of the altar to signify all those things which they flee to for refuge, and trust in, and which they make their sanctuary: