C. F. Keil and Franz Delitzsch on Numbers 8:10

Num 8:10

After this the Levites were to come before Jehovah, i.e., in front of the altar; and the children of Israel, i.e., the tribe-princes in the name of the Israelites, were to lay their hands upon them, not merely “as a sign that they released them from the possession of the nation, and assigned them and handed them over to Jehovah” (Knobel), but in order that by this symbolical act they might transfer to the Levites the obligation resting upon the whole nation to serve the Lord in the persons of its first-born sons, and might present them to the Lord as representatives of the first-born of Israel, to serve Him as living sacrifices.