Albert Barnes Commentary Psalms 124:3

"Then they had swallowed us up alive, When their wrath was kindled against us;" — Psalms 124:3 (ASV)

Then they had swallowed us up quick — There was no other help, and ruin—utter ruin—would have soon come upon us. The word 'quick' here means alive. This idea is derived from persons being swallowed up in an earthquake or by the opening of the earth, as in the case of Korah, Dathan, and Abiram (Numbers 16:32–33). Compare to Psalm 106:17. The meaning here is that they would have been destroyed as if they were swallowed up by the opening of the earth; that is, there would have been complete destruction.

When their wrath was kindled against us — Hebrew, In the kindling of their wrath against us. Wrath is often represented in the Scriptures as burning or heated—as that which consumes all before it.