You can reveal 3 "Spellbook" Spell Cards in your hand; Special Summon this card from your hand. Once per turn: You can banish 1 "Spellbook" Spell Card from your hand or Graveyard, then target 1 card on the field; destroy that target.
Special Summoning requires you have a lot of resources onhand.
Banished Spellbooks are hard to recover.
Here are some of the ways you can search High Priestess of Prophecy. Justice of Prophecy can search High Priestess with a Spellbook Spell to help with her Special Summoning; but this searching occurs during the End Phase which is very slow. Temperance of Prophecy is a much better Justice of Prophecy, Special Summoning High Priestess directly from your deck.
By the second or third turn in a Spellbook deck, you should have at least 7 Spellbook Spells in the graveyard. This will let you Special Summon High Priestess when your opponent destroys The Grand Spellbook Tower.
You can activate Spellbook of Secrets to search a Spellbook and then use that Spellbook of Knowledge in your graveyard as a cost for High Priestess’ effect. Spellbook of Eternity recovers Spellbooks banished for High Priestess’ effect cost. Spellbook of the Master can copy either of these effects to work with High Priestess.
Strength of Prophecy, Spellbook of Eternity, and Spellbook of Secrets can form a loop that gives you unlimited cost for High Priestess. Secrets searches Eternity and High Priestess banishes Secrets in your graveyard as cost. Eternity recovers Secrets and Strength returns Eternity to the deck. On your next turn you can use Secrets to search Eternity and start the loop again.
Kinda bad to open with this card, since it's either dead until you have 3 Spellbooks to reveal, or you do have 3 Spellbooks, but it also means revealing to your opponent that you have no Traps and no other monster.