Adam Clarke on Psalms 124:1

If it had not been the Lord - If God had not, in a very especial manner, supported and defended us, we had all been swallowed up alive, and destroyed by a sudden destruction, so that not one would have been left. This might refer to the plot against the whole nation of the Jews by Haman, in the days of Mordecai and Esther; when by his treacherous schemes the Jews, wheresoever dispersed in the provinces of Babylon, were all to have been put to death in one day. This may here be represented under the figure of an earthquake, when a chasm is formed, and a whole city and its inhabitants are in a moment swallowed up alive.