Jesus is the Door
A door is a means of access. The door in title is in reference to Who Jesus is. Jesus Christ alone is the door. Trying to use a way other than Christ Jesus and what He did on the Cross for mankind, makes one a thief and a robber.
The Shepherd and His Sheep
Jesus is the Shepherd. He is the Shepherd because He was the only One Who could perfectly keep the law. He is the Way to salvation. Jesus leads the sheep, believers, whosoever will, into green pastures (Truth). The Shepherd knows His sheep by name, and the sheep know His voice, and follow Him. Only a heart that truly desires to seek Him will find and follow Him. True sheep cannot be deceived by false prophets. "And a stranger will they not follow, but will flee from him: for they know not the voice of strangers (John 10:5).
"Verily, verily, I say unto you, He that enter not by the door into the sheepfold, but climb up some other way, the same is a thief and a robber. But He that enter in by the door is the shepherd of the sheep. To Him the porter open; and the sheep hear His voice: and He call His own sheep by name, and lead them out. And when He put forth His own sheep, He goes before them, and the sheep follow Him: for they know His voice (John 10:1-4).
"While it is said, Today if you will hear His voice, harden not your hearts, as in the provocation (Hebrews 3:15).