Albert Barnes Commentary 1 Samuel 13:9

"And Saul said, Bring hither the burnt-offering to me, and the peace-offerings. And he offered the burnt-offering." — 1 Samuel 13:9 (ASV)

There is a difference of opinion among commentators as to whether Saul himself offered the sacrifices prepared for Samuel, thus usurping 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 commanded him to wait until Samuel came. This is, on the whole, the more probable view, since Samuel’s rebuke says nothing about an assumption of the priesthood, as we read in the case of Uzziah (2 Chronicles 26:18).