Jesus (John 3, in speaking to the Pharisee Nicodemus about salvation) refers to the following event in Moses' day, as a type (past, see also 2 Kings 18:4), in a prophecy (yet future to Jesus and Nicodemus speaking, about Jesus' death on the Cross for Nicodemus (and us all)):
Num 21:4 And they journeyed from mount Hor by the way of the Red sea, to compass the land of Edom: and the soul of the people was much discouraged because of the way.
Num 21:5 And the people spake against God, and against Moses, Wherefore have ye brought us up out of Egypt to die in the wilderness? for there is no bread, neither is there any water; and our soul loatheth this light bread.
Num 21:6 And the LORD sent fiery serpents among the people, and they bit the people; and much people of Israel died.
Num 21:7 Therefore the people came to Moses, and said, We have sinned, for we have spoken against the LORD, and against thee; pray unto the LORD, that he take away the serpents from us. And Moses prayed for the people.
Num 21:8 And the LORD said unto Moses, Make thee a fiery serpent, 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.
Num 21:9 And Moses made a serpent of brass, and put it upon a pole, and it came to pass, that if a serpent had bitten any man, when he beheld the serpent of brass, he lived.
The serpent in this instance (John 3) refers to Jesus Christ ("even so", as Jesus equates "the serpent" with "the Son of Man" (Daniel 7:13; Matthew 16:13)), who, took upon himself the likeness of sinful flesh (Romans 8:3), and was "made ... to be sin for us" (2 Corinthians 5:21), and thus become the "propitiation" for the sins of the whole world (1 John 2:2; see also John 3:16).
Thus as the serpent on the pole was looked upon and the people were delivered from the poisonous sting and death which resulted, by merely believing God's word and acting upon it in Moses' day, so too would it be likewise in Jesus' day, when He was lifted up:
Joh_8:28 Then said Jesus unto them, When ye have lifted up the Son of man, then shall ye know that I am he, and that I do nothing of myself; but as my Father hath taught me, I speak these things.
Joh_12:32 And I, if I be lifted up from the earth, will draw all men unto me.
Joh 12:33 This he said, signifying what death he should die.
Joh_12:34 The people answered him, We have heard out of the law that Christ abideth for ever: and how sayest thou, The Son of man must be lifted up? who is this Son of man?
Zec_12:10 And I will pour upon the house of David, and upon the inhabitants of Jerusalem, the spirit of grace and of supplications: and they shall look upon me whom they have pierced, and they shall mourn for him, as one mourneth for his only son, and shall be in bitterness for him, as one that is in bitterness for his firstborn.
Isa_45:22 Look unto me, and be ye saved, all the ends of the earth: for I am God, and there is none else.
Thus, the devil (the real serpent), satan, and his venom of lies and sin and selfishness began (Romans 16:20) to be crushed (Genesis 3:15) by Jesus Christ at Calvary.
So, in short, Look unto Jesus, the "author (in the sense of one who begins a project, see Luke 14:28) and finisher of our faith" (John 3:15):
Heb_12:2 Looking unto Jesus the author and finisher of our faith; who for the joy that was set before him endured the cross, despising the shame, and is set down at the right hand of the throne of God.
Php_1:6 Being confident of this very thing, that he which hath begun a good work in you will perform it until the day of Jesus Christ: