Numbers 21:8

And the Lord said unto Moses, in a command which was adapted to the situation and was of great typical significance, Make thee a fiery serpent, cast a figure which is an exact reproduction of one, and set it upon a pole, like a standard; and it shall come to pass that every one that is bitten, when he looketh upon it, shall live. The reference is, of course, not to a casual glance, which even an unbelieving Israelite might cast upon the figure, but to the look of faith resting upon the divine promise. For such a look was an acknowledgment of sin, a longing for deliverance from its penalty, and a trusting in the means appointed by God for healing.