At one point in John Bunyan's Pilgrim's Progress, the hero of the story, Christian, finds himself talking with two sketchy fellows named Formalist and Hypocrisy. Like Christian himself, they insist, they are on their way to the Celestial City, and they're quite certain they'll make it because many in their country have gone this way before.
Of course, the names give it away. Formalist and Hypocrisy aren't going to make it to the city at all.
The first time Christian sees the two men, they are tumbling over the wall that runs alongside the narrow path Christian is on. He of course recognizes that this is problematic, since he knows that the only legitimate way into the narrow path was through the Wicket Gate, which in the story symbolizes repentance and faith in the crucified Christ.
If we make it onto the path, what's it matter which way we got in? If we are in, we are in. You are on the path, and you came in at the gate; we are on the path, and we climbed over the wall. So how are you any better off than we are?
Christian warns the men that the Lord of the city has decreed that everyone who enters the Celestial City must enter the narrow path through the gate, and he shows them a scroll he was given there, which he must present at the gate of the city in order to gain entrance. "I imagine," Christian says, "that you lack this, because you didn't come in at the gate."
Bunyan's point was to show that the only way to salvation is through the Wicket Gate — that is, through repentance and faith. It's not enough to be navigating the path of the Christian life. If a person doesn't come in through that gate, he is not truly a Christian.