From Rohan Healey's Greeks to Geeks: Practical Stoicism in the 21st Century -
"Question: What about God and all that stuff, do I have to have faith? Do I have to change my religious beliefs? Is there any praying or any other weird rituals I have to do? And what about an afterlife?
Answer: The original Stoics were Pantheists, believing that nature is God, that this 'God' pervades all the universe and is found in everything; however it is nor necessary to be a full-on Pantheist to enjoy practical benefits of Stoic philosophy. Everyone from the most devout religious practitioner to the most scientific of atheists and everyone in between can enjoy Stoicism. As the Stoics are fond of saying, 'be it God or atoms,' it matters not."
It is interesting to note that in a time when most people were polytheistic in their outlook, the Stoics tended toward Unitarian and Pantheist frameworks of understanding.