5:6 water and blood. The coming of Christ by water refers to His baptism, when He testified through His immersion unto death and emergence unto life about His coming death and resurrection. At this introductory act of His public ministry, the Spirit came on Him, as a dove, and the Father audibly acknowledged Him from heaven (Matthew 3:16-17). Then He came with the same testimony on the cross, no longer in figure but in reality, shedding His blood in sacrificial death, only to rise in triumph on the third day. Thus, both the water and the blood testify of death—His death for our sins. Note also that when the spear pierced His dead body, it was stressed that “forthwith came there out blood and water” (John 19:34).
5:6 Spirit that beareth witness. There is also the witness of the Holy Spirit, who likewise bears testimony of the sacrificial love of Christ to the world (see John 15:26, where He also—as here—is called “the Spirit of truth”). Thus the baptismal water, the shed blood and the Spirit of truth all give a united testimony concerning the saving work of Christ.