John Gill Commentary 1 Samuel 15:31

"So Samuel turned again after Saul; and Saul worshipped Jehovah." — 1 Samuel 15:31 (ASV)

So Samuel turned again after Saul
Though he before said he would not, (1 Samuel 15:26) yet he did, changing his mind, as he might without being chargeable with a lie; and he also might have an impulse from the Lord so to do, and which he did not in order to worship with Saul, which it does not appear he did, but rather the contrary; but that Saul might not be despised by the people, and his authority lessened, while he continued king; and that he might do what Saul had neglected to do, destroy Agag: and Saul worshipped the Lord; alone, by offering sacrifice to him.