Charles Ellicott Commentary Numbers 8:10

"and thou shalt present the Levites before Jehovah. And the children of Israel shall lay their hands upon the Levites:" — Numbers 8:10 (ASV)

Shall put their hands upon the Levites. —The same phrase is here used as in Numbers 8:12, and elsewhere, of the offerer who was required to lay his hand upon the victim which he offered in sacrifice. By this symbolic act, the obligation which rested upon the whole nation in regard to the dedication of the firstborn was transferred to the Levites, who were from then on to be dedicated to the service of the Lord, and given over to the priests as the representatives of the Lord.