Mark 1:9

1:9 In those days. According to John 2:20, one of Jesus’ earliest acts following His baptism took place when the rebuilding of the temple was in its forty-sixth year. Since Herod began reconstruction in 19 b.c., Jesus was baptized in about a.d. 27.

baptized by John. Jesus knows this to be part of the divine plan “to fulfill all righteousness” (Matt. 3:15), by which, in His humanity, He identifies fully with the human condition, and begins the process of bearing the sins of humanity. See theological note “The Baptism of Jesus.”