What should I do about a religious player who refuses to accept the existence of multiple gods in D&D? [on hold]

I am working on a campaign which I am going to run for a group of friends, all of whom are new to D&D.

I was discussing available classes with one of the players, more specifically classes with access to magic and the differences between them. I brought up that paladins draw their powers from the gods. The player was offended by this and made a comment about how there is only one god and no one should be allowed to play as a paladin. I tried to explain that it’s a fictional universe in which there are different gods, to which the player responded, “No.”

I really don’t know how to deal with this, because I would prefer not to limit the classes or my world creation because of this, but I also don’t want to kick this player out because they’re a close friend of mine and it would probably cause a conflict I don’t want.

I’m already invested in 5e and playing that, so I also don’t want recommendations for other systems.