John Wesley on 1 Samuel 15:29

Strength of Israel - So he calls God here, to shew the reason why God neither will nor can lie; because lying proceeds from the sense of a man's weakness, who cannot many times accomplish his design without lying and dissimulation; therefore many princes have used it for this very reason. But God needs no such artifices; he can do whatsoever he pleaseth by his absolute power. Repent - That is, nor change his counsel; which also is an effect of weakness and imperfection, either of wisdom or power. So that this word is not here used in the sense it commonly is when applied to God, as in Jer 11:1 - 23, and elsewhere.