God and Necessity: A Defense of Classical Theism argues that the God of classical theism exists and could not fail to exist. The book begins with the definition of key terms and analysis of the concepts of God and necessity. Extended examinations of the ontological, cosmological, and teleological arguments are given. The last chapters give an extended exposition and defense of the transcendental argument for God's existence. It is shown that rival accounts of the existence of universe, the Brute Fact and the Necessary Universe theories completely fail, while Necessary Deity, the concept of God existing in all possible worlds, succeeds. Only the latter can account for reality as it is, and can account for knowledge and justification.
Highly recommend chapters 4 and 8 especially, though the other chapters are broadly helpful. I primarily give this 4 stars as opposed to 5 because this book is from 1997 so some of the terms are outdated, making things a little confusing. I also wish he spent more time engaging with the Scholastic ontology because I'm pretty sure his objection to divine simplicity (that virtual distinctions don't work for properties since the properties entail different things at root) has been examined by Thomists via the doctrine of analogy. That being said, this book was very helpful overall and I highly recommend it.
Should add that I emailed Dr. Parrish afterwards and he's a very kind man. His enthusiasm and generosity compels me to read his other works.