What does John 10:9 mean?

Sheep pens in Jesus' era were constructed with a single, narrow opening. This allowed the gatekeeper to control which animals got in or out. When allowed by the gatekeeper, shepherds could call to their flocks, who would respond only to the voice of their own shepherd. Jesus has used this well-known concept to explain His ministry to His religious critics. This verse continues the second of three analogies related to shepherding.

Here, again, Jesus claims "I am the door." So far as this metaphor goes, Jesus means He is the gatekeeper—the person who controls access to the pen. He is also the opening, the single means by which the sheep can move in or out. This also reflects the nature of God, as Moses heard from the burning bush (Exodus 3:14).

This analogy brings several layers of meaning. First and foremost, it is only through the door that the sheep can "be saved." This uses a Greek term, sōthēsetai, which implies something being kept safe, healed, or rescued from destruction. This is very dramatic terminology for literal sheep, though the pen was their best protection from wild animals. Jesus' statement, then, is unusually direct in its spiritual implications. Jesus is that door, and the only door, an idea often repeated in the New Testament (John 14:6; Acts 4:12).

Closely related to this, the door—Jesus, in this case—is what separates all sheep into two basic groups. Sheep are either "in" or "out"; they are "saved" or "unsaved." There are no other categories, and no other options. This, also, supports the New Testament's consistent teaching that Jesus Christ is the one and only means by which any person can be eternally saved.

Also, some interpreters see this as a reference to Jesus leading people out of Judaism and into its intended fulfillment, Christianity.