Tom's selfish, greedy approach toward religion also manifests itself in his financial decisions. When Tom barters away his soul to the devil and agrees to be a usurer for him, he immediately begins to think of schemes to perhaps keep his earthly wealth and his intangible soul. He goes to church regularly, not so that he can better his community or help others--he thinks of it as a way to provide "insurance" against the devil's requirement. Similarly, Tom carries around his Bible to ward off the devil or his "employees." Tom's religion does not illustrate a desire to be closer to God or to better his ways; rather, he views religion as a means to earning more (from taking advantage of church members) and protecting himself.
Likewise, Tom's attitude toward his business activities focuses solely on how to accumulate the most wealth. When members of the community come to Tom seeking mercy, Tom treats them as the devil eventually treats Tom. He denies them any compassion and benefits from their loss, just as the devil will soon benefit from Tom's rash promise.
In the end, Tom's self-serving, short-term thinking about religion and business causes exactly what he feared most.