What does John 19:35 mean?

John does not explicitly name himself, preferring the typical third-person view of ancient literature. However, there are ample clues that he is identified by phrases such as "whom Jesus loved" (John 13:23), "the disciple whom [Jesus] loved," (John 19:26), and so forth. John began this gospel by declaring that the writer had witnessed these events first-hand (John 1:14). This is a claim John will repeat in his letters (1 John 1:1–2; Revelation 1:1–2).

In this case, the disciple in question was at the foot of the cross (John 19:26) when Jesus died (John 19:30). He was also there to see soldiers break the legs of the other condemned men (John 19:32), but not Jesus, who was already dead (John 19:36). He was there to see a spear stabbed into Jesus' side, resulting in a gory flood of bodily fluids (John 19:34).

John's reason for including this declaration seems to have two purposes. In one sense, this expresses the horror of what He saw. Intense awareness that one has seen something awful is part of the trauma eyewitnesses experience. After seeing some significant event, most especially distressing ones, witnesses often emphasize the fact that they saw it: "it happened right in front of me," "I watched the whole thing," "I saw everything," and so forth. John saw His beloved Master maimed and murdered, then watched a soldier mutilate the corpse. That would have been harrowing, to say the least.

The other reason John emphasizes this point is the main purpose of his gospel in the first place (John 20:30–31). The disciples of Christ wanted others to know the truth, and to be confident in it (1 John 5:13). Others might deny some of these events, but John can say with absolute certainty that he was there when it happened (2 Peter 1:16).