Albert Barnes Commentary Numbers 27:18

"And Jehovah said unto Moses, Take thee Joshua the son of Nun, a man in whom is the Spirit, and lay thy hand upon him;" — Numbers 27:18 (ASV)

In whom is the spirit. Compare Genesis 41:38. Joshua was endowed by God with the requisite spiritual qualifications for the office. Moses, however, was to lay his hands upon him, both to confer formal and public appointment, and also to confirm and strengthen the spiritual gifts already bestowed. The previous reception of the inner grace did not dispense with that of the outward sign; compare the case of Cornelius (Acts 10:44–48) and Paul’s baptism after his miraculous conversion (Acts 9:18).