The sacrifice which Samuel planned was meant to be accompanied by a fellowship meal (see 1 Samuel 9:19–24). This suggests that it was going to be a thanksgiving/fellowship offering (Leviticus 3:1–17; Leviticus 7:11–21).1 Samuel, Jesse, and his sons will leave together for the feast only after the youngest has also joined them.2
11 Then Samuel said to Jesse, “Are all your sons here?” And he said, “There remains yet the youngest, but behold, he is keeping the sheep.” And Samuel said to Jesse, “Send and get him, for we will not sit down till he comes here.”