The principle of identity is crucial in understanding the nature of being and God's existence as it underpins the coherence and intelligibility of reality. It asserts that a thing cannot be and not be at the same time, ensuring consistency in existence. This principle connects to the principle of raison d’être, which states that everything has a reason for its existence. Together, they form the foundation for metaphysical realism, positing that the intellect's object is being, and that the essence and existence of a thing are identical.
This connection is vital for understanding God's existence. By applying these principles, it is argued that the contingent and changing world requires a transcendent, unchanging cause, which is God. The principle of identity ensures that this cause is not a contradiction, and the principle of raison d’être necessitates that this cause is the ultimate reason for everything's existence. Thus, the principles of identity and raison d’être provide a logical and metaphysical framework for comprehending the nature of being and the existence of God.