As I'm sure you know, St. Maarten isn't known for its snorkeling. However, some of the best snorkeling seems to be at Divi; it's probably half an hour to Pinel from Divi. Not sure what church you are looking for, but many people walk to downtown Philipsburg from Divi, where there is a church. The walk back is uphill so if you aren't in good shape, you could get a taxi (plentiful in Philipsburg) back to Divi.

Just one suggestion.