1 Samuel 7:9 - Joseph Benson’s Commentary on the Old and New Testaments

Samuel took a sucking lamb For after a lamb was eight days old, it was fit to be sacrificed to God, Exodus 22:30; Leviticus 17:27. And offered it for a burnt-offering For though he was not a priest, nor this place appointed for sacrifice, yet as a prophet he had authority from God to build an altar anywhere and offer sacrifices. Thus other holy men, Gideon and Manoah, were warranted to offer extraordinary sacrifices, in places which God had not before appointed. And thus we read of an altar he built in another place, 1 Samuel 7:17, as Elijah did in following times. And Samuel cried unto the Lord He made intercession with the sacrifice. So Christ intercedes in virtue of his satisfaction. And in all our prayers we must have an eye to his great oblation, depending on him for audience and acceptance. And the Lord heard him Probably God answered Samuel as he did Manoah, by sending fire from heaven to consume the sacrifice, in testimony of his acceptance of it.