Here the perfect High Priest steps out from among His people - sinless, yet he permits himself to be purified, washed as a sinner. He fully identifies with us in every way. Here the sin offering is prepared for slaughter. God's Lamb is washed in preparation for the shedding of His blood. Jesus' baptism in the Jordan river puts Him on the road to Calvary and the cross.
Baptism means repentance from sin and forgiveness of sin.
People came to John confessing their sins to be baptized into the forgiveness of sins. Christ came as the Lamb of God, the unblemished Sacrifice, the perfect whole burnt offering. In His Baptism, Jesus stood shoulder to shoulder with sinners, some the worst and most despised. Yet Jesus was not ashamed to stand in solidarity with them. He had no sin to confess, no sinfulness to turn away from.