Full Idea
Plantinga reformulates Malcolm's argument thus: 1) There is a possible world in which there exists a being with maximal greatness, 2) A being has maximal greatness in a world only if it exists in every world.
Gist of Idea
A possible world contains a being of maximal greatness - which is existence in all worlds
Source
report of Alvin Plantinga (The Nature of Necessity [1974], p.213) by Brian Davies - Introduction to the Philosophy of Religion 4 'b Descartes'
Book Reference
Davies,Brian: 'An Introduction to the Philosophy of Religion' [OUP 1993], p.59
A Reaction
This is only Plantinga's starting point, which says nothing about the nature of God, but only that this 'great' being exists in all worlds. I would like to know why it is a 'being' rather than a 'thing'. Malcolm says if it is possible it is necessary.