Numbers 8:9

And thou shalt bring the Levites before the tabernacle of the congregation: and thou shalt gather the whole assembly of the children of Israel together:

The children of Israel ... Since it was plainly impossible that the whole multitude of the Israelites could do this, a select portion of them must be meant. This party, who laid their hands upon the Levites, are supposed by some to have been the firstborn, who, by that act, transferred their special privilege of acting as God's ministers to the Levitical tribe; and by others to have been the princes who thus blessed them. It appears from this passage that the imposition of hands was a ceremony used in consecrating persons to holy offices in the ancient, as, from the example of our Lord and his apostles, it has been perpetuated in the Christian Church.