Commentaries:
In a sense, this is David's baptism, in which he was separated from all his brothers—in effect, from all the people of the tribes of Israel. This anointing consecrated him as "king," just as we, too, have been separated from the world and set apart as God's people. Like David, who did not immediately function as king over Israel, we are to be kings and priests of God in the resurrection, in His Kingdom (Revelation 5:10; 20:4-6; I Peter 2:9-10).
Richard T. Ritenbaugh
Psalm 133 (1998)