Jesus tells Nicodemus that as Moses lifted up the serpent in the wilderness, so the Son of Man must be lifted up. The comparison assumes the story of Numbers 21, where dying Israelites look toward the raised bronze serpent and live.
John then uses 'lifted up' with a characteristic double force.
Numbers 21 describes poisonous serpents among Israel and God's instruction that Moses make a bronze serpent and place it on a standard; those who look at it in response to God's provision live. In John, the Greek verb for lifting up can describe physical elevation while also carrying the sense of exaltation.
Later passages explicitly connect Jesus' being lifted up with the manner of his death, making crucifixion and exaltation paradoxically converge.
The scriptural background shows that Jesus is not merely predicting the mechanics of execution. He presents his coming elevation as God's life-giving provision for people facing death.
John's irony is profound: the cross, designed as public humiliation, becomes the place where the Son is 'lifted up' and where his divine mission is revealed.