Matthew 3:13-17
Then Jesus went from Galilee to the Jordan River to be baptized by John. But John tried to talk Him out of it. "I am the one who needs to be baptized by you," he said, "so why are you coming to me?" But Jesus said, "It should be done, for we must carry out all that God requires." So John agreed to baptize Him. After His baptism, as Jesus came up out of the water, the heavens were opened and He saw the Spirit of God descending like a dove and settling on Him. And a voice from heaven said, "This is my dearly loved Son, who brings me great joy."
John 1:32-34
Then John testified, "I saw the Holy Spirit descending like a dove from heaven and resting upon Him. I didn't know He was the one, but when God sent me to baptize with water, He told me, 'The one on whom you see the Spirit descend and rest is the one who will baptize with the Holy Spirit.' I saw this happen to Jesus, so I testify that He is the Chosen One of God."
John the Baptist preached a message of repentance, and people of every background came to be baptized to show that they had repented of their sins. When Jesus came to be baptized by John, John tried to talk Him out of it. Jesus had no sin, and John thought that Jesus ought to baptize him; why should He ask John to baptize Him? Jesus was the Chosen One of God and didn't need to repent of sin.
In this context, to repent is to give up an old way of life and take up a new way of life. Jesus wasn't being baptized to repent of any sins but to change the course of His life. After His baptism and temptation in the wilderness, Jesus began His ministry and preached His message of repentance. After Jesus was baptized He changed everything about His life. His baptism was an anointing for ministry.
"It should be done, for we must carry out all that God requires." I believe that when Jesus said this to John, He meant that He must be baptized in order to begin His ministry and do what God required. God required Jesus to spend time ministering to the masses as well as developing close relationships with a select few of His followers so that they could carry on the message of the kingdom after Jesus was gone. To do all of this Jesus had to be baptized first; He changed His life and exchanged the quiet life of a carpenter's son for ministry.
In getting baptized, Jesus committed Himself to God's will and accepted what was going to inevitably happen at the close of His ministry. He accepted a mission of salvation for mankind through great sacrifice. He became a servant and lived a life of conflict and persecution that led to a painful death.
But that was not the end of Jesus' mission; God had something extraordinary planned that exceeded all expectations. Jesus defeated death and completed His mission on earth.
