Clerics DO NOT need to worship a god. Clerics can believe in a philosophy so strongly that they can manifest their powers.
— Todd Kenreck (@ToddKenreck) March 9, 2020
For the people in the back. "a cleric might instead serve a cosmic force, such as life or death, or a philosophy or concept, such as love, peace, or one of the nine alignments." – Dungeon Master's Guide
— Todd Kenreck (@ToddKenreck) March 9, 2020
If that’s the rules by which your group is operating with I’m all for it. I won’t have issue with a GM that uses God’s or not as influence and/or direct empowerment for their followers. To me it’s a flavor thing that offers context that I enjoy. I use Forgotten Realms settings almost exclusively as a GM/DM and enjoy the rich history and detail that the God’s of the realms offer (or higher powers). So long as the PC has a distinct persona/philosophy that is easily understood then I’m good with it. If the Cleric/Paladin or religious zealot PC has a distinct philosophy I like putting “encounters” that challenge those tenants within their PC’s belief system. If a player can roleplay and present “their character’s system of beliefs” well enough in the game then it’s all good. I’ve run a game during the “Time of Troubles” and the “self-powered” cleric wouldn’t be an easy fit for that “specific narrative setting”. Still, I could see making it work if that’s the concept a player might insist upon.
Clerics most definitely must worship a god. My table, my rules.
Why? Besides you say so. Why do you say so?