As has been said, a ground loop is a likely culprit.
Power conditioners have their place, but I’ve never had one eliminate hum when added.
Does your church use fluorescent lights? If so - that’s likely contributing, if it isn’t the outright cause. Fluorescent bulbs emit what is called 60 cycle hum. It can either be transmitted through the power circuit, or more commonly it’s coming through your pickups.
Lots of good tips here. Lights can always be an issue. THe most critical issues I have endures were induction loops. But that would affect all guitars / basses on that specific venue.