John 3:14,15

Ver 14. And as Moses lifted up the serpent in the wilderness, even so must the Son of man be lifted up: 15. That whosoever believes in him should not perish, but have eternal life.

CHRYS. Having made mention of the gift of baptism, He proceeds to the source of it, i.e. the cross: And as Moses lifted up the serpent in the wilderness, even so must the Son of man be lifted up.

BEDE; He introduces the teacher of the Mosaic law, to the spiritual sense of that law; by a passage from the Old Testament history, which was intended to be a figure of His Passion, and of man's salvation.

AUG. Many dying in the wilderness from the attack of the serpents, Moses, by commandment of the Lord, lifted up a brazen serpent and those who looked upon it were immediately healed. The lifting up of the serpent is the death of Christ; the cause, by a certain mode of construction, being put for the effect. The serpent was the cause of death, inasmuch as he persuaded man into that sin, by which he merited death. Our Lord, however, did not transfer sin, i.e. the poison of the serpent, to his flesh, but death; in order that in the likeness of sinful flesh, there might be punishment without sin, by virtue of which sinful flesh might be delivered both from punishment and from sin.

THEOPHYL. See then the aptness of the figure. The figure of the serpent has the appearance of the beast, but not its poison: in the same way Christ came in the likeness of sinful flesh, being free from sin. By Christ's being lifted up, understand His being suspended on high, by which suspension He sanctified the air, even as He had sanctified the earth by walking upon it. Herein too is typified the glory of Christ: for the height of the cross was made His glory for in that He submitted to be judged, He judged the prince of this world; for Adam died justly, because he sinned; out Lord unjustly, because He did no sin. So He overcame him, who delivered Him over to death, and thus delivered Adam from death. And in this the devil found himself vanquished, that he could not upon the cross torment our Lord into hating His murderers: but only made Him love and pray for them the more. In this way the cross of Christ was made His lifting up, and glory.

CHRYS. Wherefore He does not say, The Son of man must be suspended, but lifted up, a more honorable term, but coming near the figure. He uses the figure to show that the old dispensation is akin to the new, and to show on His hearers' account that He suffered voluntarily; and that His death issued in life.

AUG. As then formerly he who looked to the serpent that was lifted up, was healed of its poison, and saved from death; so now he who is conformed to the likeness of Christ's death by faith and the grace of baptism, is delivered both from sin by justification, and from death by the resurrection: as He Himself said; That whosoever believes in Him should not perish, but have everlasting life. What need then is there that the child should be conformed by baptism to the death of Christ, if he be not altogether tainted by the poisonous bite of the serpent?

CHRYS. Observe; He alludes to the Passion obscurely, in consideration to His hearer; but the fruit of the Passion He unfolds plainly; viz. that they who believe in the Crucified One should not perish. And if they who believe in the Crucified live, much more shall the Crucified One Himself.

AUG. But there is this difference between the figure and the reality, that the one recovered from temporal death, the other from eternal.