Final answer:
In John Bunyan's 'Pilgrim's Progress', Christian has a key called Faith that opens all doors, symbolizing the power of belief to overcome life's challenges.
Step-by-step explanation:
The question refers to John Bunyan's Christian allegory Pilgrim's Progress, where the protagonist, Christian, possesses a key called Faith that is said to open all doors. This key symbolizes the strong belief in Christian values and tenets that will help the believer navigate through the difficulties of life, much like a key that opens all locks. The references provided seem to evoke the symbolism of light and truth in this allegorical text, pointing to the way material things can lead to spiritual enlightenment, with Christ being the ultimate 'true door' to salvation and truth in Christian belief.