Augustine of Hippo — as excerpted in the Catena Aurea on John 10:1-5

“(Tr. xlv. 2. et sq.) Or thus: Many go under the name of good men according to the standard of the world, and observe in some sort the commandments of the Law, who yet are not Christians. And these generally boast of themselves, as the Pharisees did; Are we blind also? But inasmuch as all that they do they do foolishly, without knowing to what end it tends, our Lord saith of them, Verily, verily, I say unto you, He that entereth not by the door into the sheepfold, hut climbeth up some other way, the name is a thief and a robber. Let the Pagans then, the Jews, the Heretics, say, “We lead a good life;” if they enter not by the door, what availeth it? A good life only profiteth, as leading to life eternal. Indeed those cannot be said to lead a good life, who are either blindly ignorant of, or wilfully despise, the end of good living. No one can hope for eternal life, who knows not Christ, who is the life, and by that door enters into the fold. Whoso wisheth to enter into the sheepfold, let him enter by the door; let him preach Christ; let him seek Christ’s glory, not his own. Christ is a lowly door, and he who enters by this door must be lowly, if he would enter with his head whole. He that doth not humble, but exalt himself, who wishes to climb up over the wall, is exalted that he may fall. Such men generally try to persuade others that they may live well, and not be Christians. Thus they climb up by some other way, that they may rob and kill. They are thieves, because they call that their own, which is not; robbers, because that which they have stolen, they kill.”