He said; he declared his intention in express words, as Exodus 32:10, and elsewhere. In the breach: God had made a hedge or wall about them; but they had made a gap or breach in it by their sins, at which the Lord, who was now justly become their enemy, might enter to destroy them; which he had certainly done, if Moses by his prevailing intercession had not hindered him. See Deuteronomy 9:12, Deuteronomy 10:10. It is a metaphor from a besieged city, where the enemy endeavours to make a breach in the walls, and thereby to enter into the city; which he will do, unless some valiant champion stand in the gap to oppose him.
Related Commentaries of Psalms 106:23
Psalms 106:23
23 Therefore he said that he would destroy them, had not Moses his chosen stood before him in the breach, to turn away his wrath, lest he should destroy them.