I cannot say that I am quite satisfied with it. For instance: why did God choose to effect this possible world? Presumably because it pleased Him. Why did it please Him? Presumably the answer has something to do with His nature. But it seems to me such an answer implies that God must have effected this possible world, since God's nature is not itself effected but rather that by which all other things are effected. God's nature is determinative. That in turn implies this is the only possible world, in which case the problem reasserts itself: how does God know counter-factuals if this is the only possible world? Vexing...
God's decree to effect this possible world implies that this possible world is entailed in God's decree to maximally manifest His glory; that is, given God's purpose to maximally manifest His glory, God necessarily must have decreed to effect this possible world.
For God to act in a manner which would not bring Himself maximal glory… would constitute a contravention of the divine nature, and since God cannot deny Himself, God’s actions too are determined [by His own, immutable nature].
Why did God decree to maximally manifest His glory? I don't see any other possible conclusion than something similar to this or what I said to my friend. In fact, to say there are multiple possible worlds is simply to say God's instantiation of this possible world was not necessary. On this supposition, can there be a reason God instantiated this possible world? Would not such a reason imply the necessity of the instantiation? If not, then is not the alleged reason an arbitrary one?
2. Let us suppose God had actualized a different possible world; after all, if God's actualization of this world wasn't absolutely necessary, He could have chosen to actualize a different possible world. But this means God's knowledge is not eternal, since His knowledge [of what is the actual world] would not be necessary.