this makes no sense to me, why does it have to exist in every world because it exists in one? thats like saying if i sit in one chair i sit in every possible chair"
In this context, "maximally great" means a being which has maximal excellence in every possible world. It would then exist in every possible world, according to the one making the definitions and playing these particular word games. You're right that it makes no sense, which is a good indication that the initial assumption(s) is deeply flawed.
that's a tautology though, if you rewrite that with that definition of maximal excellence it says:
"3. If a being exists in every possible world, then it exists in every possible world."
Also I'm assuming 'every world' is along the lines of M theory, if so I still don't get why something that exists in one facet of a multiverse has to exist in all.
Makes no sense to me, seems deeply illogical.