As the gods were active in the world and as action implies reaction, they could be influenced by appropriate rituals, mostly ancient. Not for control, for the lessor cannot control the greater, but for harmony and unity. With appropriate actions, the gods would help purify the soul, help her rise.
This was Theurgy, “divine working”, rather than theology, “divine knowledge” and it was the province of Iamblichus, a Syrian philosopher.
which makes sense. If there are gods effecting the world then they must be effected by it in return. Of course, some didn’t like it. Magic, they called it.