Expositor's Bible Commentary Commentary John 1:33

"And I knew him not: but he that sent me to baptize in water, he said unto me, Upon whomsoever thou shalt see the Spirit descending, and abiding upon him, the same is he that baptizeth in the Holy Spirit." — John 1:33 (ASV)

The second aspect of John’s witness to Jesus (see comment on v.29) concerned the title “Son of God.” This aspect was related to the work of the Holy Spirit, who both authenticated the mission of Jesus and was the seal of his work in individual lives. John announced that Jesus would impart the Holy Spirit to his followers. To “baptize with the Holy Spirit” means that just as the common experience of baptism in water signified repentance and confession of sin, so the indwelling of the Holy Spirit is the seal and dynamic of the new life. Repentance and confession are the conditions on which the believer receives the gift of the Spirit (cf. Acts 2:38; Galatians 3:2; Galatians 5:16–25). The manifestation of the presence of the Spirit in Jesus’ case was visible , though this gospel records the Baptist’s later reflection on that event.

John the Baptist’s solemn avowal that he had seen the descent of the Spirit on Jesus and that he is "the Son of God” is the climax of his testimony. The significance of the title can be best understood in the light of 1:18 (see comment). John’s emphatic declaration was the reason why the disciples left him to follow Jesus.