Collect the books together in one place. Ideally you will be able to use a space where the books can remain undisturbed between sessions.
Decide on a classification system to categorize your books. The Dewey Decimal System is the most commonly used library system in the world and as a result anyone using your church library is likely to be familiar with it. The Dewey system allocates each book a number; all religious books have a number between 200 and 299.
Sort the books out into subject areas, using the categories laid out in the Dewey Decimal system. Each subject area has its own number so, for example, books dealing with the life of Jesus Christ go together under "232," while you can group the texts of hymns under "245" and books about church furnishings under "247."
Put a small sticker on the spine of each book labeled with the number of the Dewey Decimal classification that book belongs to. For example, you would label copies of the Bible with the number 222. If any of your books are old or valuable, consider covering them with a plastic sleeve.
Place the books on the shelves in order of categorization. To make it easier to find a book in a particular category, put them onto the shelves in alphabetical order within each category. You might find that some are too large for the shelves available to you; if this is the case, remove the larger books and put them -- in classification order -- on a separate shelf marked "Oversize."
Stick a label on each shelf, listing the numbers of the books on that shelf.
Print a copy of the "200" series of the Dewey Decimal system and put it on the wall of the room the books will be kept in to help other users locate what they're looking for.