1. If God (a maximally great being) exists, then God exists necessarily.
2. It is logically possible that God exists.
3. If it is logically possible that God exists, then there is a possible world in which God exists.
4. In any possible world in which God exists, God exists necessarily.
5. To exist necessarily “in” any possible world is to exist necessarily.
6. To exist necessarily is to exist in all logically possible worlds.
7. Therefore, God exists.