In his Gospel, John has three subtle moments of foreshadowing about the Cross. All of which involve Jesus calling himself a snake.
In the first, right before his famous “For God so loved the world” line, Jesus compares himself to a bronze snake on a pole. “Just as Moses lifted up the snake in the wilderness, so the Son of Man must be lifted up, that everyone who believes may have eternal life in him.” (John 3:14-15) This is in reference to a rather strange story from Numbers 21. The main point being that people are in danger of death because of their own rebellion against God, so the antidote (like all actual antidotes) is the means of death itself.
In the second Jesus says “When you have lifted up the Son of Man, then you will know that I am he and that I do nothing on my own but speak just what the Father has taught me.” (8:28) Like in Numbers, this strange solution to the problem of death was God’s idea. And like Moses, Jesus is merely being obedient, as unorthodox and outlandish as the remedy may sound.
In the third, Jesus makes clear that the healing he is to offer is for anyone and everyone. “And I, when I am lifted up from the earth, will draw all people to myself.” After which, just to make sure his readers don’t miss the point, John adds, “He said this to show the kind of death he was going to die.” (John 8:28)
Of all the mortal danger one might encounter out in the wilderness of this world, the most deadly threat is one’s own self. So when John describes Jesus carrying his own cross, he means that Jesus is getting ready to do for the whole world what Moses did for the people of Israel.
