John points out several prophesies that were fulfilled at the time of Jesus' crucifixion. Before the prophesies come to pass, they can appear contradictory, but afterward they are clearly understood. For instance the prophesy, "They divided my garments among them, and for my clothing they cast lots" (Psalm 22:18). At face value it would seem both could not be accurate, either you divide something evenly between parties, or you roll the dice to see who gets all of it.
Of course from this side of the cross we know thy divided his robe into quarters but his tunic was such a fine work they rolled the dice to see who took it home (John 19:23-24).
Another prophesy that John points out is that none of Jesus' bones were broken (Psalm 34:20; Numbers 9:12; John 19:36); and that the soldiers pierced Jesus' side with a sword (Zechariah 12:10).
It is not logical to think someone considered an enemy Rome could control the actions of soldiers in the course of his own crucifixion (I.e. dividing his robe, casting lots for his tunic, not breaking his bones, stabbing him after he was already dead). If someone was foolish enough to try and bribe soldiers what would keep the soldiers from taking the money and not doing anything they promised. And what would be the purpose of such a bribe anyway?
Only God could know and control what would happen. John points these things out so that all who read his letter know that Jesus was indeed the promised Messiah, "the Son of God and believing you might have life in his name" (John 20:31).
