# Invocation ritual
For the invocation of an artifact, see invoke.
In NetHack, the Invocation ritual is an act performed by applying three specific items on the vibrating square in a certain order: the Candelabrum of Invocation, the Bell of Opening, and the Book of the Dead. The invocation ritual is required to ascend and complete the game, being the only way to gain access to Moloch's Sanctum.
All the objects involved in the ritual are unique and indestructible, with the exception of the candles placed in the Candelabrum - any seven candles will do. Vlad's Tower is the only guaranteed source of candles in the game, but there are various additional sources - randomly generating them, purchasing from a shop (usually Izchak's), finding them in a monster's inventory, polypiling from other tools, or even wishing for them if necessary. 

Contents

1 Performing the Invocation

1.1 Mistakes during the invocation

2 After the ritual
3 History
4 Origin
5 References

Performing the Invocation
The typical invocation sequence is as follows:

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Player successfully completing the invocation. The tiger will drown the next turn.

1. Stand on the vibrating square.

You feel a strange vibration under your feet.
2. Light the non-cursed Candelabrum of Invocation, which must have 7 candles placed in it.

The candelabrum's candles burn brightly! The candelabrum glows with a strange light!
3. Ring the non-cursed, charged Bell of Opening.

You ring the Bell of Opening. The Bell of Opening issues an unsettling shrill sound...
4. Finally, read the non-cursed Book of the Dead.

You begin to recite the runes. You turn the pages of the Book of the Dead... The floor shakes violently under you! The walls around you begin to bend and crumble! You are standing at the top of a stairwell leading down!
Lighting the Candelabrum and ringing the Bell can be performed in either order, but the Book must come last. The Candelabrum will remain lit for much longer than the effect of ringing the Bell, so if you are concerned about being interrupted, it is slightly safer to ring the Bell second - ringing the Bell first has the slight advantage of conserving one turn of light from the Candelabrum.
Performing the ritual will reveal the staircase down into Moloch's Sanctum in place of the vibrating square and create a ring of fire traps immediately around you in a one-square radius - a massive moat of a roughly 4-5 square radius will also appear around you. 

Mistakes during the invocation
If you perform the ritual incorrectly, you might receive a message, or even raise the dead.
There are a couple of methods to remembering the proper order - the most important points are that all three items must be non-cursed, and that the Book must be used last.
Sascha Wostmann's guide to remembering the steps is: 

Make some light to read by.
Ring the bell to get the attention of the audience.
Read the book to them.
Another way to remember the order of steps is to apply each item according to its depth in the dungeon: Bell (quest), then Candelabrum (Vlad's Tower), and finally Book (the Wizard's tower).

After the ritual
After the moat and fire traps are created, nearby monsters may be caught on top of one of the fire traps or drown in the moat - this breaks pacifist conduct.
Once you have access to the staircase, you can levelport into the Sanctum, which can bypass the graveyard and sometimes even put you right into the temple.
After the ritual is performed, none of the items are needed to win the game, and you can safely drop them if you wish. However, they do have uses outside of the ritual. Keep in mind that you cannot put them in containers, and carrying them will not necessarily deter covetous monsters from stealing your quest artifact.[1]

The Candelabrum makes an effective light source, shining one square further than a lamp - some players may take the Candelabrum with them, typically for jumping on the Astral Plane. Remember to extinguish it after the ritual if you do so, and don't re-light it too often, as it loses half its remaining life span each time.
The blessed Book of the Dead can be used to pacify undead as a chaotic character, even while adhering to illiterate conduct.
The charged Bell of Opening works as a wand of secret door detection to quickly enter Moloch's Sanctum, though it may take up to four uses to find the hidden door in the walls of the Sanctum.
History
The invocation ritual is first introduced to the game in NetHack 3.1.0.

Origin

Wikipedia has an article about:
Bell, book, and candle

The motif of "Bell, Book and Candle" originated as a Catholic ritual of excommunication by anathema, although some works often portrayed it as connected with exorcism (e.g., the Terry Pratchett/Neil Gaiman novel Good Omens). One notable occurrence of the motif is in the 1985 computer role playing game Ultima IV: Quest of the Avatar: the player must find the Bell of Courage, the Book of Truth, and the Candle of Love in order to enter the Abyss, the final dungeon of the game.[2] A bell, book, and candle similarly provide access to the lowest levels of Hell in the classic text adventure Zork.[3]

References

↑ wizard.c in NetHack 3.4.3, line 275

↑ Wiki article on the Great Stygian Abyss at ultimacodex.com

↑ Zork 1 walkthrough