1 Samuel 15:29 - Matthew Poole's English Annotations on the Holy Bible

He calls God the Strength of Israel; partly, to show the reason why God neither will nor can lie; because lying is a weakness, and proceeds from the sense of a man's weakness, because he cannot many times accomplish his design without lying and dissimulation; which therefore many princes have used for this very reason. But, saith he, God needs no such artifices; he can do whatsoever he pleaseth by his absolute power, and hath no need to use lies to accomplish his will. Partly, to show that Israel should be no loser by Saul's loss, as he might vainly imagine, because he had saved them from their enemies on every side, 1 Samuel 14:47. For not Saul, but God, was the Strength and Protector of Israel, and he would continue to save them when Saul was lost and gone. And partly, to assure Saul that God would execute this threatening, because he wanted not strength to do it, and none could hinder him in it. Nor repent, i.e. nor change his counsel; which also is an effect of weakness and imperfection, either of wisdom or power.