1. Jesus uses the story of the bronze serpent from Numbers 21 to teach Nicodemus about salvation. As the Israelites were saved by looking at the serpent on the pole, so people are saved by believing in Jesus who was lifted up on the cross.
2. Anyone who believes in Jesus will not perish but have eternal life, just as the Israelites who looked at the serpent lived. Belief requires a spiritual transformation or new birth.
3. Jesus is referring to himself as the Son of Man who was lifted up to save all those who believe in him, in the same way the Israelites were saved by gazing at the bronze serpent.