In the D&D world of Faerun, there are a pantheon of gods whose existence is concrete and not in question. People call on these deities to perform magic and miracles, and it always works... well, unless they have shitty concentration, and orcs are swinging clubs at their heads. But in that case, the failure is on them, and not on the god who really actually exists.
The definition of "faith" is "belief without proof." When there exists a shit-ton of evidence for something, it is impossible to have faith in that thing, by definition. A cleric in Faerun cannot have faith in his god any more than I on Earth can have faith in the Pythagorean theorem. If I stamp my foot and fold my arms and say, "A squared plus B squared does NOT equal C squared!" what difference does it make? The theorem still works. Who cares what I think? Similarly, in Faerun, if someone claims not to believe in a god or gods, he's not having a "crisis of faith." He's being an idiot. The god(s) will continue to exist whether he likes it or not.
So, if a divine-powered NPC ever starts nagging your character about "faith," feel free to deliver a solid smack upside the head, and tell your DM to knock it off. The clerics/paladins of Faerun should instead be concerning themselves with things like adherence to their deities' dogmas, and loyalty to the deity one chooses to worship. No Flavor-of-the-Month postulants, please.
P.S. If I lived in Faerun, I would totally be a Dawnbringer of Lathander.