When in your bookcase, this text is called "Prayer of Deliverance from Poisons".
Below is the text you can read from within the book.
Being the full and proper prayer against morbidities of the flesh caused by venoms and potions of both a natural and mystic origin. Take up your blessed symbol of the Saradomin, cast in silver. Hang it about thy neck, where all may see it and thus know of your devotion. Pray in a loud, clear voice to the Saradomin for relief from that which ails you. Appropriate calls for aid should be accompanied by a sacrifice of prayer energy, with deadlier venoms requiring a greater sacrifice. Should the supplicant lack piety, they will not be cured. Should they possess a measure of piety equal or even greater than that which assails them, the poison will reduce or even cure, while a like amount of Prayer energy will be taken to do this. Be wary: should the supplicant only partially remove the venom thought the application of prayer, their body must still bear the brunt of its wickedness. Also...(The rest of the book seem to have been vandalised, charred and slightly bled upon.)
After completion of the associated quest, if you have unlocked the entire Hub track, this item can be retrieved from the Quest Item Storage chest at the Quest Point Caravan if lost or destroyed. Otherwise, a new one can be obtained from the bookcase in the monastery or the bookcase in your Player-Owned House made through Construction.
The ability to cure you of poison is the only reason to keep this item, however, poison is not a problem for all players. Especially when you can use antipoison or add the Venomblood perk to your armor using Invention. As such, it can be destroyed or kept as you desire.