Disclaimer; I've only read Anselm and Leibniz, and am just trying to piece together the discrepant sources around.
Premise 1: There are many worlds.
Definition 1: "x necessarily exists if and only if every essence of x is necessarily exemplified" (From the article)
Premise 2: Existence is good.
Definition 2: God is the being Good-er than whom cannot be conceived.
Sub-Conclusion 1: God if he exists, by definition is good, and by supposition necessarily exists because existence is good. He necessarily exists because if he did not, then a being good-er than him could be conceived (ie, one that existed), and that being would then not be god.
sub-conclusion 2: Because there are many worlds, there exists one with a being good-er than whom cannot be conceived. Therefore, this is a being whose existence is necessary.
Consider then, that God's existence would not be necessary, if the world that god governed was not necessary, because that world could, or could not exist, and so God could, or could not exist, and god's existence would not be necessarily be exemplified.
Therefore The world in which God exists must be necessary to our world, and by consequence, God's existence must be necessary to our world.
If someone who has actually read him could give me some feedback as to whether this is fairly close to what he means, I'd appreciate it.