How does Tom tries to assume the role of a devoted religious man in "The Devil and Tom Walker"?
Toward the end of the story, after Tom has struck his bargain with the devil and received his riches, he begins to grow old. We read that he becomes "thoughtful" and "anxious," even that he feels "regret" over what he's done.
Knowing that he gave his soul to the devil in order to get his wealth, he tries to think of a way to back out of the deal and decides to put on a public show of zealous religious belief. Most of this attempt is described by the narrator in a single paragraph of the story. As we read that paragraph, we get a delicious little twinge of dramatic irony: we know for certain that there's no way the hypocritical, greedy, rotten Tom is getting out of his Faustian deal, and now he's desperate to try anyway. But his attempt is all about show. Remember, Tom is rotten to the core.
So, in public every Sunday, he prays to God "loudly and strenuously," as if he could push aside the other worshipers on his way into Heaven. He also becomes obsessed with pointing out his neighbors' sins, as if that would help his own seem like less of a big deal in the eyes of God. (Readers call to mind at this point a messy young child who, hoping to avoid getting in too much trouble, points at the other children to tell on them as if it could deflect attention away from himself.) He even carries a Bible around with him.
Despite all this bluster, we can tell for certain that it's insincere. How? Because he keeps making bargains at work to take advantage of his customers. If he really wanted to present himself as a reformed soul, he'd show kindness and generosity instead. So it's particularly telling that the devil really does come to claim Tom's soul the moment that Tom is about to make even more money by financially ruining his "friend."