John Lightfoot on John 3:14

[And as Moses lifted up the serpent, &c.] The Jews dote horribly about this noble mystery. There are those in Bemidbar Rabba, that think that the brazen serpent was not affixed to a pole, but thrown up into the air by Moses, and there to have settled without any other support.

"Moses put up the serpent for a sign; as he that chastiseth his son sticks up the rod in some eminent place, where the child may see it, and remember."

Thou shalt remove the mischief by that which did the mischief; and thou shalt heal the disease by that which made thee sick. The same hath R. Bechai; and both confess that it was a miracle within a miracle. But it is not for a Jew to understand the mystery; this is the Christian's attainment only.