My best advice is take him aside and let him know you need to talk to him and when you tell him just be open and honest and start at the begining. let him know you are struggling with the feelings that come with incontinence and having to wear diapers. Remember you are not alone in dealing with IC issues rhere are millions of us who are back in diapers as an adult for bladder or bowel issues.
there is no shame in needing to wear protection for a medical issue, the first time I had to tell some ione was hard but it gets easier, and as a pastor he should be understanding and supportive ( its one of the requirements)

When my boss found out I need to wear he understood and infact the medication he is taking for his diabetes is causing him bladder issues as well but fortunately its frequent trips to the bsthroom to pee so he can relate to my bladder issues.
once people around you daily know the stress of dealing with incontinence starts to diminish as you no longer need to hide your medical issue.