Suffer it to be so
Why one who needed no repentance should insist upon receiving a rite which signified confession (Matthew 3:6) and repentance (Matthew 3:11) is nowhere directly explained. It may be suggested:
(1) That Jesus was now to receive His anointing with the Holy Spirit (Matthew 3:16) unto His threefold office of Prophet, Priest, and King. In the Levitical order (Exodus 29:4-7) the high priest was first washed, then anointed. While Christ's priestly work did not begin till He "offered Himself without spot to God" (Hebrews 9:14) and His full manifestation as the King-Priest after the order of Melchizedek awaits the kingdom
( See Scofield) - (Genesis 14:18)
yet He was then anointed, once for all.
(2) But John's baptism was the voice of God to Israel, and the believing remnant responded (Matthew 3:5). It was an act of righteousness on the part of Him who had become, as to the flesh, an Israelite, to take His place with this believing remnant.
righteousness
( See Scofield) - (1 John 3:7).