Then Jesus said to them again, "Most assuredly, I say to you, I am the door of the sheep. All who ever came before Me are thieves and robbers, but the sheep did not hear them. I am the door. If anyone enters by Me, he will be saved, and will go in and out and find pasture.

It is only by this door, that is, Christ Jesus, through faith, that we can enter into a relationship with God. There is only one door; meaning there is no other way into heaven. There is only one shepherd, meaning there is no religion; except that of following Christ, that is the Messiah.