Matthew Poole and continuators on John 3:14

14 ¶ And as Moses lifted up the serpent in the wilderness : even so must the Son of man be lifted up .

The History of the lifting up of the Serpent in the Wilderness, we have, Numb. 21.8, 9. the people being stung with fiery Serpents, as a righteous Judgment of God for their sins, as a merciful remedy, God commanded Moses, v. 8. Make thee a fiery Serpent, [that is, the Image or Representation of one of those fiery Serpents], and set it upon a pole, and it shall come to pass, that every one that is bitten, when he looketh upon it, shall live; this brazen Serpent in the Wilderness was a lively Type of Jesus Christ. Our Saviour having before spoken of the New Birth as necessary to those who shall be saved; here comes to shew it in the causes, and instanceth first in the meritorious, then in the instrumental cause, the meritorious cause was his Death; he saith, That look as the Serpent was lift up in the Wilderness:

So he, who was the Son of man must be lifted up; that is, dye upon the Cross: the Phrase is used twice more in this Gospel, chap. 8.28. and 12.32, 34. an allusion doubtless to this Type. Yet Mr. Calvin thinks the lifted up here, more properly interpreted of the Doctrine of the Gospel, and by the Preaching of it; and others apply it to Christs ascension into Heaven; and this he tells Nicodemus must be, for the fulfilling the Scripture, and the Counsels of his Father.