The Bible is a set of Christian scriptures, consisting of 73 books of the Old and New Testaments (66 in Protestant Bibles).
The Bible item instantly killing Mom, Mom's Heart, and It Lives! is a reference to the epilogue of The Binding of Isaac when the Bible hits Mom's head, knocking out or killing her.
In the original Binding of Isaac, using The Bible on Isaac and ??? would kill Isaac.
This item is one of the only two ( five) in the game that work towards 2 transformations (Bookworm and Seraphim) and is the only activated item that does that. The other ones are Hive Mind, Skatole, Magic Mushroom, and Parasitoid.
With an ID of 33, The Bible is the very first active item on the ordered ID list, likely due to its plot relevance.
3DS The icon of The Bible as seen on the lower 3DS screen.
The Bible's splash image which appears when it's activated.
If The Bible is used on Mom with the Broken Remote trinket, it will not kill Mom and will instead teleport Isaac randomly to another room. However, this still unlocks The Halo as if Mom was killed with the Bible.