More than likely, the metaphorical meaning of this section title relates directly back to a Biblical connection. It is fairly common literary (and religious) knowledge that the moment Adam and Eve sinned in the book of Genesis is referred to as "The Fall." This term denotes humanities fall from God, fall from grace, and ultimately, eternal separation from paradise. According to the New Testament, the only forgiveness for "The Fall" came through the unconditional and sacrificial love of Jesus Christ, who paid for the sins of all mankind through his death on the cross.
Keeping that in mind, consider Jean Valjean's actions in this section of the novel. Though unfairly imprisoned for a very long time, at this point, Valjean has finally been awarded his freedom. As an ex-convict, he is shunned by everyone in the small town through which he walks, until he comes upon the house of the bishop. The bishop not only takes him, but feeds him, provides a clean bed, and talks to him like a man.
Much like Adam and Eve in the garden of Eden, Valjean is treated with unconditional kindness and love. Also like Adam and Eve, he repays this kindness with a sin. Adam and Eve ate of the forbidden fruit. Similarly, Valjean robs the bishop of his only valuable possessions. And though it was many years later in which God provided graceful forgiveness for humans through Jesus, the bishop's forgiveness is immediate. When Valjean is arrested and brought back to verify the robbery, the Bishop explains that the silver was a gift and not stolen at all.
The forgiveness that Valjean experiences (and subsequent life change as a result) parallels that of the Christian journey, humans who deserve nothing but receive unconditional love, grace, and forgiveness.