Anything ecclesiastical is related to a church. The Bible is a book used in ecclesiastical environments.
Ecclesiastical things have to do with religions, specifically churches, especially Christian churches. Pews, readings from the Bible, members of the clergy, and stained glass windows are all part of the ecclesiastical world. If a politician gets support from a church, that's an ecclesiastical endorsement. If you believe in the separation of church and state, you definitely don't want ecclesiastical teachings to inform the way laws are made. Secular is the opposite of ecclesiastical.
