John the Baptist said to the people,
” I indeed baptize you WITH WATER UNTO REPENTANCE but he that cometh after me is mightier than I, whose shoes I am not worthy to bear: he shall baptize you WITH THE HOLY GHOST, and with fire:” (Matthew 3:11 KJV)
In Matthew, it is it making plain that the purpose of John’s baptism was to provide an occasion for Jewish people to confess their sins and repent (defined in Greek it was penned as ‘changing their mind‘) and get right with God. The Jewish people were relying on Law keeping and their lineage from Abraham (Matthew 3:9) to save them and John the Baptist was ‘preparing the way’ for the message of Salvation by what Christ would do as the coming Messiah; pay for the sins of the whole world to save all who would believe. A drastic repentance which is a drastic change of belief for the Jewish people.
In Matthew 3, then we see Jesus coming on the scene as John the Baptist said He one day would:
“13 Then cometh Jesus from Galilee to Jordan unto John, to be baptized of him.
14 But John FORBAD HIM, saying, I have need to be baptized of thee, and comest thou to me?”
We see here that John is saying to Jesus that Jesus has no need to be baptized unto repentance. Jesus has no sins to change His mind about!
“15 And Jesus answering said unto him, Suffer it to be so now: for thus it becometh us TO FULFILL ALL RIGHTEOUSNESS. Then he suffered him.”
Jesus fulfilled ‘all righteousness’. He never sinned as He was God in the flesh. Yet, He came to pay for our sins on the cross as the once for all payment (Hebrews 10:10) for the sins of the whole world (1 John 2:2).
Jesus as Messiah (The Word) became human and joined fallen humanity, though without having sin, and he was providing righteousness for us in sharing their water baptism of REPENTANCE, not relying on Law keeping or being of the lineage of Abraham. Jesus humbled Himself in perfect righteousness so we, in belief on Him (John 3:14-18, 1 Cor. 15:1-4) could receive the righteous which comes by faith, not works (Eph. 2:8-9, Philippians 3:8–9).
By being baptized unto repentance He fulfilled all righteous. Did Jesus deserve to die shedding His blood on the cross when He had NO SIN? NO!
Why did He then? To fulfill all righteousness and be the ONE FINAL SACRIFICE (Hebrews 10) to pay the sin debt we all have, MAKING US through His sacrifice, the righteous of God, in Christ ( Cor. 5:21).
John water baptized UNTO REPENTANCE. It was an outward expression of the people’s change of mind about how to be saved. The water baptizing itself is not what saved them once Christ came. It is changing their minds (which is the literal Greek definition of the English word ‘repent’) from a false salvation by their self righteous efforts of Law keeping and relying on Abraham’s lineage, to belief on Christ.
Jesus was water Baptized to show them it was true and in doing so fulfilled all righteousness. A blessing to those changing their mind.