Was Socrates a theist or atheist? How does he justify his position?

He was a theist. He believed that the gods existed and he was the divine missionary. Although whether or not he believed in the Olympian gods has been contested, but this is not a major part of his philosophy and it is true that the ancient Greeks often took the existence of the divine as a given. Also, he had a bit of a mystical side, this is evident from his dialogues, in which he would often use such analogies.