In John 3:14, Jesus tells the learned Nicodemus that just as Moses lifted up the serpent in the wilderness, even so must [He], the Son of man be lifted up, basically speaking about the the manner of his crucifixion (lifted on the Cross).

But why did Jesus have to be lifted up? Jesus was lifted up so that He can lift us up; lift us out of the horrible pit, out of the miry clay (Psalm 40:2); lift our souls out of the grave (Psalm 30:3); and most importantly Jesus was lifted up so that He could draw all men [and women] unto himself (John 12:32). Jesus was lifted up so He can lift us up. The question is are you drawn to and unto Jesus?

John 3:14 (KJV)
14 And as Moses lifted up the serpent in the wilderness, even so must the Son of man be lifted up:

John 12:32 (KJV)
32 And I [Jesus], if I be lifted up from the earth, will draw all men unto me.

Psalm 30:1,3 (KJV)
1 I will extol thee, O LORD; for thou hast lifted me up, and hast not made my foes to rejoice over me.
3 O LORD, thou hast brought up my soul from the grave: thou hast kept me alive, that I should not go down to the pit.