The 6 god books are books held in place of a shield. A player first receives a damaged book and needs to add 4 god pages to make a complete god book. Once a page has been put into a god book, the page cannot be retrieved.
After killing the Dagannoth Mother in the Horror from the Deep quest, you will receive a "Rusty casket." Speak to Jossik about this chest, and he will ask you to read what the chest says. You can choose from the three main gods: Saradomin, Guthix, or Zamorak. For whichever god you choose, you will get a "Damaged book" of that god. When wielded, this book provides +5 to prayer. However, this isn't the book's true potential. Torn pages that are missing from your Damaged book can be found and put back in to complete the book. You can acquire torn pages by completing Treasure Trails, or by buying them from adventurers who have gained them as a reward from the treasure trails. Torn pages are uniquely numbered (1 through 4) and coloured to match only one god's book. Once you have added all four torn pages back into your Damaged book, it becomes a new book depending on which god it is for. Saradomin's Damaged books become holy books, Guthix's Damaged books become book of balance, and Zamorak's Damaged books become unholy books. As a part of a later update, players can now obtain and restore 3 new damaged books. Armadyl's Damaged books becomes the book of law, Bandos' Damaged books becomes the book of war, and Zaros' Damaged books become the book of darkness. You can now go back to Jossik and buy any different damaged book for 5,000 coins, without having to complete the first one.
A completed god book provides bonuses to Attack and Defence depending on which god it is for. Also, a completed god book allows a player to preach and perform ceremonies, such as blessing, last rites, and wedding rites. A completed god book can also be used to bless silver symbols if the player's Prayer level is 50 or higher. Blessing a symbol with a god book expends four Prayer points. A Holy book can bless holy symbols, an Unholy book can bless unholy symbols, and a Book of Balance can bless both (though it costs six Prayer points instead of four). To complete a God book players need to obtain four god pages. Once these pages are put in they cannot be taken out.
If a player loses their book, they can go back to Jossik to have it returned, complete with all the pages it had beforehand. The player can hold more than one of the same book at a time, making completed god books a great option for risky wilderness activities. Alternatively, players can purchase one from Perdu for 12,000 coins.