Our blessed Lord was now declaring that He was to be lifted up, as the serpent had been lifted up. As the brass serpent had the appearance of a serpent and yet lacked its venom, so too, when He would be lifted up upon the bars of the Cross, He would have the appearance of a sinner and yet be without sin. As all who looked upon the brass serpent had been healed of the bite of the serpent, so all who looked upon Him with love and faith would be healed of the bite of the serpent of evil.
—from The Life of Christ by Fulton Sheen, Ch. 7: Nicodemus, the Serpent, and the Cross