Jesus pointed out to those who had confronted the man born blind that He was the Good Shepherd. He used an allegory of the sheepfold to teach an important lesson on the kingdom. The sheepfold, a place of safety represented the church.
God was the keeper of the door by which Christ, the Good Shepherd would enter with His sheep. Christ also represented Himself as the door through which the sheep, who were His disciples, would enter. Gentiles, who did not count with the Jews, were the other sheep that Jesus would bring into the sheepfold later.
The thief and robber represented the Jewish leadership which opposed Jesus. False teachers, who would put themselves up as equal to God or Christ were represented as the hireling and strangers.
One can enter the sheepfold or church only through Jesus, the Door.