With this verse, Amos sees an image of destruction of a temple. The tops of the pillars (capitals) and the bottoms (called thresholds) would shake and collapse. Amos makes use of a merism which indicates the total destruction of the structure. The vision then is one of a people gathering in a building for worship only for that building to collapse and everyone to perish.1
1 I saw the Lord standing beside the altar, and he said: “Strike the capitals until the thresholds shake, and shatter them on the heads of all the people; and those who are left of them I will kill with the sword; not one of them shall flee away; not one of them shall escape.