Also attached to Christianity, and religion in general, is a feeling by many people that there are too many rules and “thou shalt not’s” that you must follow in order to be a member. This is made light of in the scene where Arthur asks the monks for the Holy hand grenade. Very specific directions on how to use it are read from the “Book of Armaments.” Also represented is the tendency of lay people to get those directions wrong.
ARTHUR: Consult the Book of Armaments!
GOD: Arthur! Arthur, King of the Britons! Oh, don't grovel! If
there's one thing I can't stand, it's people groveling.

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MAYNARD: Armaments, Chapter Two, Verses Nine to Twenty-One.
BROTHER: "And Saint Attila raised the hand grenade up on high,
saying, 'Oh, Lord, bless this thy hand grenade that with it thou
mayest blow thy enemies to tiny bits, in thy mercy.' And the Lord
did grin, and people did feast upon the lambs, and sloths, and
carp, and anchovies, and orangutans, and breakfast cereals, and
fruit bats, and large --"
MAYNARD: Skip a bit, Brother.
BROTHER: "And the Lord spake, saying, 'First shalt thou take out
the Holy Pin. Then, shalt thou count to three, no more, no less.
Three shalt be the number thou shalt count, and the number of the
counting shalt be three. Four shalt thou not count, nor either
count thou two, excepting that thou then proceed to three. Five is
right out. Once the number three, being the third number, be
reached, then lobbest thou thy Holy Hand Grenade of Antioch towards
thou foe, who being naughty in my sight, shall snuff it.'"
MAYNARD: Amen.
ALL: Amen.
ARTHUR: Right! One... two... five!
???: Three, sir!
ARTHUR: Three! [boom]
ARTHUR: Sorry--
GOD: And don't apologize. Every time I try to talk to someone
it's "sorry this" and "forgive me that" and "I'm not worthy". What
are you doing now!?
ARTHUR: I'm averting my eyes, oh Lord.
GOD: Well, don't. It's like those miserable Psalms -- they're so
depressing. Now knock it off!
ARTHUR: Yes, Lord.
GOD: Right! Arthur, King of the Britons -- you're Knights of the
Round Table shall have a task to make them an example in these dark
times.
ARTHUR: Good idea, oh Lord!
GOD: 'Course it's a good idea! Behold! Arthur, this is the Holy
Grail. Look well, Arthur, for it is your sacred task to seek
this Grail. That is your purpose, Arthur -- the Quest for the Holy Grail.
ARTHUR: A blessing!
LAUNCELOT: A blessing from the Lord!
GALAHAD: God be praised!