Didache [It’s Greek for teaching. Sounds like did-uh-kay] is my only non-fiction book. It’s a curriculum for confirmation, and covers things like what Christians understand about God the Father, Son, and Holy Spirit, the church, Christian worship, the Bible, marriage, death & resurrection, baptism, Eucharist, ministry, etc. It’s still in-process, but I’ve used it in my confirmation classes for the past several years.