Is There a Metaphysically Necessary Being?

I've had something that i wanted to talk about for a while, and so i don't know of a better time to bring it up. So when you have an analytic truth, or you have a necessary truth, it's got to entail or the falsity of that proposition has to entail a contradiction. But in my mind, it seems like work sort of begging the question here, because if god is a metaphysically necessary being, then the proposition god exists is going to entail the proposition, god exists and god cannot not exist. Yet, it's begging the question, if you assume it, without motivating your assumption.