Albert Barnes Commentary 1 Samuel 7:9

"And Samuel took a sucking lamb, and offered it for a whole burnt-offering unto Jehovah: and Samuel cried unto Jehovah for Israel; and Jehovah answered him." — 1 Samuel 7:9 (ASV)

Samuel’s preparation for intercessory prayer, namely, offering an atoning sacrifice, is most significant . The term used here for a “lamb” does not occur in the Pentateuch; indeed, it is only found anywhere else in Isaiah 65:25. The offering is in accordance with Leviticus 22:27.

The Lord heard him — A more precise translation is “The Lord answered him.” The “answer” was not simply the granting of the requested deliverance, but the great thunder (1 Samuel 7:10), which was “the voice of the Lord”—the same voice with which the Lord answered Moses (Exodus 19:19; Psalms 99:6).