Fidelity is a complicated and abstract idea. It has elements of trust, loyalty, love and even faith. In the Bible, there are some instances where the Greek word for faith and fidelity is the same. So what does this tell us?
It means faith and fidelity are related, if not the same. One should not have faith only, but it can also be measured through daily experiences. For instance, one can say he has faith in God, but this claim does not show in his daily activities and decisions. He may have faith, but the fidelity is missing.
Fidelity is what makes our claim credible. Words and beliefs are difficult to understand for an outsider, but if he sees the outward experience and result of that faith, he may even become interested to know more.