In the Ancient Near East, the flock would be put into small pens and the shepherd would sleep in the gate at night. This way he could keep the sheep safe in the pen and predators out. He would make himself the door to the pen. Jesus is using an illustration that would be familiar to His hearers.
If you want to enter a building, you go through the door. The way we enter the church of Christ is through Jesus. It is only by faith that we can come to God and truly be part of his people. Jesus is the only door by which you can enter into salvation (John 14:6)
Have you come into the church through faith in Jesus Christ? Is your Christianity a real spiritual truth? Or is it just your traditions, just your culture? There are many false doors into the church that will only lead to death and separation from God. There is only one door that leads to God and life. It is Jesus himself. Have you gone through Jesus to enter salvation and the Church of God?
Consider: Matthew 7:13