Richard Beck has a useful debunking and re-bunking of Anselm’s (in)famous “ontological argument” for the existence of God:
Few find the ontological argument persuasive. It seems too cute and quick. Seems a bit fishy. And yet, some find the argument persuasive and the argument has been given a fair amount of logical and philosophical attention, then as now.
Personally, I’m one of those who don’t find the ontological argument persuasive. And yet, how I think about God has a family resemblance to the ontological argument.
At its heart the ontological argument has us imagine a horizon of “greatness” and “perfection.” The argument then goes on to say that existence must be, necessarily, a part of that vision. Maybe, maybe not. But in one sense it really doesn’t matter. Because I think that horizon of “greatness” and “perfection” can do much of the work we want from any conception of God, with or without existence.