“And Iesus answering, said vnto him, Suffer it to be so now: for thus it becommeth vs to fulfill all righteousnesse. Then he suffered him.”
1611 King James Version (KJV)
3:15 It becometh us to fulfil all righteousness - It becometh every messenger of God to observe all his righteous ordinances. But the particular meaning of our Lord seems to be, that it becometh us to do (me to receive baptism, and you to administer it) in order to fulfil, that is, that I may fully perform every part of the righteous law of God, and the commission he hath given me.
Mt 3:15 Suffer [it to be so] now. The term "now" implies that the relation of Jesus to his work made it proper that now he should be baptized. It is true that baptism was for sinners; Jesus was sinless; but he humbled himself, accepted the burden of human duties, and must set a perfect example to men. He obeyed the Jewish law, and it was needful also that he obey the Divine rite that John had inaugurated. Thus it becometh us. In order to fulfill all righteousness, show forth a perfect obedience, set a perfect example, it became him to submit to the institution of baptism, and it became John to administer it to him. "Us" refers to Jesus and John.