1 Samuel 13:9 - Albert Barnes' Notes on the Bible

There is a difference of opinion among commentators whether Saul himself offered the sacrifices prepared for Samuel, thus entrenching upon the priest’s office; or whether he ordered the priests to sacrifice, as Solomon did. In the latter case his sin consisted in disobeying the word of God, who had bidden him wait until Samuel came. And this is, on the whole, the more probable; since Samuel’s rebuke says nothing of any assumption of priesthood, such as we read in the case of Uzziah 2 Chronicles 26:18.