Two days ago, I mentioned that Sr. Ann, in Karina Fabian's Antivenin, really knows her Scripture. I've been thinking about one verse she quoted: "Then the LORD sent venomous snakes among them; they bit the people and many Israelites died." (Numbers 21:6) In the Book of Numbers, the cure for the snakes punishing the Israelites was a bronze snake held up before them. The cure for the snakes was a snake. In the story, the sisters of Our Lady of the Rescue find the solution to the real snakes oppressing them - anti-venom. The cure for the snakebites came from snakebites (or snake fangs, at least). The cure for the snakes was, again, a snake.
Jesus referred to this verse right before the famous John 3:16. When He tells us "For God so loved the world that he gave his only Son...", this passage from Numbers is the context in which He's speaking. God so loved the world that He gave us Jesus lifted up on the cross before us. "(J)ust as Moses lifted up the serpent in the desert, so must the Son of Man be lifted up, so that everyone who believes in him may have eternal life" (John 3:14-15).
The cure for snake venom comes from snake venom. The cure for the Israelite's snakebites was a snake lifted before them. And the cure for what ails us - for sin - is the same thing lifted up before us. Snake for snake, sin for sin (cf 2 Cor 5:21). Our sin, all our sin, was lifted up on the cross with Christ and expiated by His Blood. In a way, His precious Blood is our antivenin.