Matthew 3:13 - Coke's Commentary on the Holy Bible

To be baptized him— By this he intended to do an honour to John's ministry, and to conform himself to what he appointed for his followers. It was for this last reason, that he drank of the sacramental cup. See Diodati. And certainly our Lord's baptism tended to promote the ends both of his own mission and of his forerunner's, as it established the authority of both. It established John'smission; great honour being done him by the Messiah's receiving his baptism. It established our Lord's mission also; for after he was baptized, the testimonies of the Spirit and voice from heaven, were given him in the presence of the multitude assembled at Jordan. That these testimonies should have been given him on this occasion, rather than on any other, was fit, because it was an august manner of opening our Lord's ministry; was the most public occasion which could be found; and pointed him out as the Messiah to the Baptist, who was thereby qualified for the principal duty of his mission. See Macknight.