What is most instructive in Bunyan’s allegory is how Christian and Hopeful finally find the way of escape. Christian says:
“What a fool I have been, to lie like this in a stinking dungeon, when I could have just as well walked free. In my chest pocket I have a key called Promise that will, I am thoroughly persuaded, open any lock in Doubting- Castle.” “Then,” said Hopeful, “that is good news. My good brother, do immediately take it out of your chest pocket and try it.” Then Christian took the key from his chest and began to try the lock of the dungeon door; and as he turned the key, the bolt unlocked and the door flew open with ease, so that Christian and hopeful immediately came out.
What was the key? It was called “Promise.” God has given us “his precious and very great promises” (2 Peter 1:4).