The symbolism is clear. Jesus is foretelling a truth to Nicodemus: “Just as…so…” Look upon the “symbol of death” and believe in the true healing power of God’s word, and that symbol becomes for you a “symbol of life.” When Good Friday arrives, this symbolism reaches its climax. Our faith is tested to the extreme. Can this dead body represent new life for us? Of course we know the rest of the story – we know that Easter is right around the corner. We know that the Crucifix, with the body of Jesus nailed to it, is indeed the Symbol of Life. But it calls for us to get in touch with our deepest beliefs, with our core of faith. And it calls for a repentant heart, as we gaze on this scene of an agonizing Messiah who brings us salvation through our faith in Him.
Jesus makes this element of trusting the Incarnation, and confirms the Gospel preaching. Sacred art is only true when its form corresponds to its particular vocation: evoking and glorifying the mystery of God. Stained glass windows are particularly effective in confirming Gospel preaching.
Jesus makes this element of trusting faith crystal clear for his listeners. Immediately after this story of the serpent, he says “God loved the world so much that he gave his only Son, so that everyone who believes in him may not be lost but may have eternal life” (Jn 3:16). God allowed the making of images that pointed symbolically toward salvation by the incarnate Word: so it was with the bronze serpent, the ark of the covenant, and the cherubim, for examples.
Religious worship is not directed to images in themselves, but under their distinctive aspect as images leading us on to God incarnate (St. Thomas Aquinas).