There can be an internal explanation: the existence of the first cause is explained inherently if its existence is part of its essence. — A Christian Philosophy

To me, "essence" suggests a set of necessary and sufficient properties that uniquely identify an existing, individual object. Existence isn't a property; it implies there are objects in the world that lack it - which is absurd.

Perhaps you mean something else. Is so, explain what you mean, and why anyone should accept such a metaphysical framework. I'm on the lookout for contrivances that are devised to rationalize a God to the exclusion of a purely natural first cause.