Yesterday on the blog we talked about John’s hesitance to baptize Jesus. We explained why John wasn’t wrong to be hesitant. So why did John eventually give in and baptize the Messiah? Jesus gives us an answer:
Matthew 3:15—But Jesus answered him, “Let it be so now, for thus it is fitting for us to fulfill all righteousness.”
There’s that word “fulfill” again. This is already the fourth time it’s been used in three short chapters in Matthew’s gospel. Patrick Schreiner reminds us that “‘Fulfill’ has a variety of meanings, and in different contexts certain aspects might be highlighted. Yet largely, we can say that it means that Jesus fills up Jewish history.... all things are brought to fruition in and through Jesus.” 
What needs to be filled up by Jesus? Righteousness. But whose righteousness? Certainly not Jesus’s! He is already sinless; His righteousness is already filled full!
Colossians 1:19 says “For in [Jesus] all the fullness of God was pleased to dwell.” The word “fullness in Colossians is from the same word group that Matthew uses for “fulfilled.” If God is fully righteous, and Jesus is fully God, then Jesus is already fully righteous.
So again, whose righteousness needs to be fulfilled? The righteousness of Jesus’ people. Think about it: have you ever repented and then gone back to the same sin? Why do we keep confessing the same sins over and over again? Because we keep sinning! Yes, we must repent, but if the effectiveness of our repentance is what saves us we’re all going to hell!
Few are better examples of this than a monk named Martin Luther. He used to spend upwards of six hours in confession with his priest, trying to make sure he confessed every single wicked thought, motivation, emotion, or deed. Finally, his priest would say, “Go do something really bad then come back and confess that!”
But Luther was right! There’s always more to confess! In fact, we may have even sinned in our confession. We might have confessed in the wrong way or for the wrong reasons. If God is holy, then no amount of confession and repentance can clean us up!
Enter Jesus. He’s wading into the Jordan river, not because He needs to be baptized but because you need Him to be baptized. Jesus is identifying with sinners. Isaiah 53:12 prophesied that Jesus would be “numbered with the transgressors.” And Jesus is doing just that. He walks into that water as if He’s a sinner needing repentance. He’s identifying with His people.
Jesus is not there to wash away His own sin, but to begin the process of washing away ours. Jesus is sharing in our baptism so we can share in His. The price paid to wash away our sins would come three years later when Jesus is immersed with another baptism. Speaking of His impending death on the cross, Jesus said in Luke 12:50—“I have a baptism to be baptized with, and how great is my distress until it is accomplished!”
There on a hill outside Jerusalem, Jesus will complete the work He began on Jordan’s muddy banks. There the Father will make “Him to be sin who knew no sin, so that in Him we might become the righteousness of God.” (2 Cor. 5:21)
Jesus’ baptism is a preview of what He came to do. He came to redeem sinners, and to do that He had to identify with them.
 Patrick Schreiner, Matthew, Disciple and Scribe: The First Gospel and Its Portrait of Jesus (Grand Rapids, Michigan: Baker Academic, 2019), 39.