Albert Barnes Commentary 1 Samuel 15:21

"But the people took of the spoil, sheep and oxen, the chief of the devoted things, to sacrifice unto Jehovah thy God in Gilgal." — 1 Samuel 15:21 (ASV)

The Lord thy God - There is an implied censure of Samuel in this phrase. Saul says that Samuel blames him for what was done in honor of Samuel’s God, as if he had more zeal for the glory of God than was felt by Samuel.