A classical Objectivist would expect such an essay to be rather brief. Once one has acknowledged that 'existence exists' is axiomatic, no further analysis or explanation is possible or necessary. No deeper explanation is to be found. If there could be one, existence would no longer be axiomatic and we would be trying to explain existence by non-existence.
Causality is a non-issue.
Causal analysis reduces to the properties of existents. New states, actions, or changes are manifestations of the identity, the properties and attributes, of existents. There ends an Objectivist discussion of the totality of that which exists. I offer these arguments as a tribute to the potency of objectivist principles consistently applied. A crucial tool, already used in previous essays, will be the non-conceptual character of 'existent infinity'.