To those who ask, Where hast thou seen the gods, or how dost thou comprehend that they exist and so worshippest them, I answer, in the first place, they may be seen even with the eyes;8 in the second place, neither have I seen even my own soul, and yet I honor it. Thus then with respect to the gods, from what I constantly experience of their power, from this I comprehend that they exist, and I venerate them.
If any ask, Where hast thou seen the Gods or how hast thou satisfied thyself of their existence that thou art so devout a worshipper? I answer: In the first place, they are even visible to the eyes. In the next, I have not seen my own soul either, yet I honour it. So then from the continual proofs of their power I am assured that Gods also exist and I reverence them.
Marcus Aurelius, Meditations XII.28. Translated by George Long (1862). The Stoic Library.