I've been designing and leading Creative Teams in sermon series graphics for 5+ years. Sermon series graphics are different than ads or a typical ad campaign. It needs to be treated as art. I believe you need to dig deep into what is at the heart of the sermon series and call that out with symbolism and substance. The designs don't need to be so black & white, there needs room for beauty and mystery. After all, sermon series graphics are seen multiple times over the course of a sermon series. It's in a way long-form storytelling. Give people something to think about and something that enriches and amplifies the sermon series.