The Son of Man must be lifted up as Moses lifted up the serpent in the desert(John 3, 15)
Jesus said to Nicodemus: ‘Do not be surprised when I say: You must be born from above. The wind blows wherever it pleases; you hear its sound, but you cannot tell where it comes from or where it is going.That is how it is with all who are born of the Spirit.’ ‘How can that be possible?’ asked Nicodemus. ‘You, a teacher in Israel, and you do not know these things!’ replied Jesus.‘I tell you most solemnly, we speak only about what we know and witness only to what we have seen and yet you people reject our evidence. If you do not believe me when I speak about things in this world, how are you going to believe me when I speak to you about heavenly things? No one has gone up to heaven except the one who came down from heaven, the Son of Man who is in heaven; and the Son of Man must be lifted up as Moses lifted up the serpent in the desert, so that everyone who believes may have eternal life in him.’(John 3,7-15)
In a famous episode of the Old Testament, when Moses raised the serpent in the desert those who looked at it were healed from poisonous bites. This was a foreshadowing of Christ on the cross who, contemplated by believers, heals from the poison of sin. How many times a day do you turn your gaze towards the crucifix, in order to save yourself from the poison of temptation?