I have found that the best way to play behind a pastor is to be fluent in all keys. I have been playing quite a number of years and I still find myself learning new things. Even though I am older I keep up with all of the latest things. My suggestion is that if you don't read, then learn. It is one of the most valuable tools that you can have. The scales and progressions can get you through any key. My pastor starts in one key and modulates all over the place. the only way I can keep up with him is to learn all progressions and in all keys. I also use the number system to remember progressions. ie. I-IV-V (1-4-5) in key of C is C-F-G, Key of F
F-Bb-C, and so on. With lot's of practice you can master any key. Using this system any key is playable. Not only does this help with playing behind pastors but also behind singers who may not sing in the same key that a song is written. Another thing to do is to learn all of the variations of the chords (Maj, Min, Dim, Augmented, Min7, Maj7, Maj9, 9, 11th 13th,) and other combinations of coloring. This will greatly enhance you playing, especially behind preachers, and also for worship flowing and praise(dance) music.