Adam Clarke on Psalms 55:19

Because they have no changes - At first Absalom, Ahithophel, and their party, carried all before them. There seemed to be a very general defection of the people; and as in their first attempts they suffered no reverses, therefore they feared not God. Most of those who have few or no afflictions and trials in life, have but little religion. They become sufficient to themselves, and call not upon God.