Found an interesting 2019 twitter thread on the issue from Ed Greenwood (creator of the Forgotten Realms setting). Here's what he has to say:
One becomes a paladin by hearing and accepting a call to holy service. That acceptance is cemented by an oath. If a paladin transgresses against their oath, the usual absolution, as the PHB states, is to seek absolution from a cleric of the same faith. Paladins DO worship deities, and like any other mortal, may receive requests from mortal priests or divine servitors, or messages directly from a deity (usually through dream-visions, or literal visions appearing to a praying paladin). So although paladins by their very nature are semi-independent agents, fighting evil as adventurers rather than being temple guards, they DO serve deities. Being a cleric or a paladin in the Realms is NOT “doing what you want as an armored killer but also having healing spells because some god likes your ilk.” Although you, as a paladin, serve a god or alliance of good gods (to literally fight evil, and do so largely ‘in your own way,’) EVERYONE in the Realms ‘believes in’ all the gods, and you as a paladin may encounter priests who expect to be able to command you. Some paladins DO act within strict church hierarches, but Player Character paladins are more the ‘operate on their own’ agents. However, if your deity commands you to do something (like obey or work with a mortal priest) and you don’t, you shouldn’t expect to retain your paladinhood. What makes you a paladin is a “sacred oath,” and therefore the support of the gods. Yes, you could disobey one god but remain a paladin by obeying the will of another, but that’s a very dangerous game. Some deities in the past were micro-management types when dealing with mortals, but increasingly all FR deities are more distant, leaving mortals more to their own devices.
