Before we can understand the Incarnation and how God did not change in the Incarnation, we must first understand the Trinity. This is certainly no easy task for quite a few reasons. First, I am writing in a limited space, so even if we could comprehend God, I would not accomplish this in so few pages.
Secondly, we cannot comprehend God, so I cannot really explain the Trinity. What I can explain is what has been revealed, but I cannot explain the Trinity and how the three persons function. Rationalists need not apply in attempting to understand the Trinity or looking at the Trinity; the Trinity is a mystery and therefore cannot be comprehended.
The third reason this is not an easy task is that while what we can know of the Trinity is substantial, space and time are limited. St. Hilary of Poitiers spent the modern equivalent of 300 pages writing about the Trinity. St. Augustine spent the equivalent of nearly 500 pages writing about the Trinity. Yet both men felt that their works were inadequate. I am using only a fraction of space to write about the Trinity as these two great thinkers did, so I am positive that my explanation will be inadequate.
Regardless of the inadequacies, I will attempt to explain the Trinity to the best of my knowledge. It is my hope that in understanding the Trinity we can gain a better understanding of the Incarnation and in so doing we can understand how Christian theology does not contradict the Damascene Cosmological argument.
We must first start with the most basic understanding of the Trinity, which is that God is one substance, but three persons. By saying persons I do not mean that they are three properties. The Father is not a part of God, the Son is not a part of God, and the Spirit is not a part of God. Each one is fully God and therefore not a part. A branch is part of a tree, but not the whole tree. A hand is part of a man, but not the whole man. A tire is part of a car, but not the whole car. The Father is the whole of God. The Son is the whole of God, The Spirit is the whole of God.
In the Trinity we have three individuals who hold individuals wills, but share the same nature and therefore their wills work as one. An example (and I stress this as an example and not an analogy) is that John and Paul share the nature of “human.” Though John and Paul are individuals and hold individual wills, they can work as one toward a common goal. I use this as an example to show that different wills can exist within the same nature and work together, but we must remember that the nature of the Trinity is not like the nature of humans. God is still one entity and one being. Whereas John and Paul are two beings, the Father, Son, and Spirit are all one Being, who we call God. To explain this is beyond human means and therefore we retreat into mystery.
While we recognize the three persons of God, we also recognize that there is one divine nature. Whatever is true of the nature is true of all the persons since all the persons share equally in the divine nature. Thus, if we say the divine nature is omniscient (that is, not ignorant) then this stands true for the Father, Son, and Spirit. Any differences found within the three are not found within the nature, but within the persons.
Some might point to the Father begetting the Son as an indicator that the Father is somehow superior (ontologically speaking) to the Son and has “more” of the divine essence, but such a difference resides in the persons. The Father begets while the Son is begotten and the Spirit proceeds. But all of this is found within the person and not the nature. When we think of sunlight, we know that the sun begets the light. While both share the same nature, one begets the other. Likewise, the heat that comes from the sun shares the same nature with the sun, but still proceeds forth while the sun itself does not proceed. Though this analogy is highly inadequate (and not an analogy, but an example), it demonstrates to show that differences can exist within the persons of the Trinity without those differences stemming from the substance.
While the Father begets, the Son is begotten, and the Spirit proceeds, all three are uncreated. All three are eternal. All three are omniscient. All three equally share in the divine attributes and it is appropriate to call them God. When we worship God, we worship the Father, Son, and Spirit.
Some might immediately object and point out that the begetting of the Son indicates a series of events. Since being begotten is an event, then God must exist within time because at some point the Son was begotten. If this is true, then the Trinitarian belief is not congruent with the Damascene Cosmological argument.
Such an understanding, however, misunderstands the concept of begetting. While for humans begetting means creation, for God it does not necessarily have to mean that. For one, the Son is eternally begotten. The begetting did not happen at some point in time, but is essential to the persons of the Father and Son. Turning back to the example of the sun, we see that the sun begets the light. But do we say that the sun came first and the light came second? Did the sun exist without light? The light is begotten from the sun for the duration of the sun’s existence, but such light is as old as the sun. Likewise, the Son is eternally begotten by the Father, meaning that his source is the Father, but such a begetting did not take place in time or space. This is not an infinite regress of actions because the action did not take place in time or space nor does it necessarily qualify as an action. Though the Son finds his source in the Father (that is what “begotten” means in reference to the Divine), this is not an action.
The same explanation stands for the procession of the Spirit from the Father. Just as the heat comes from the sun without the sun creating the heat at some later point to its existence, so too does the Spirit proceed from the Father. The Spirit is not created and then sent forth, but rather has always been a part of God, constantly sent forth, but in fellowship with both the Father and Son.
With all the talk of begetting and proceeding, how do we say that the Trinity avoids an infinite regress? It certainly seems as though these are series of events that subject God to a series of events. However, such an argument only works if the persons are parts. That is, if the Spirit is a part of God, then by proceeding we have an event because a part is being moved. However, the Spirit is God and not a part, therefore in procession nothing is moved. God “moves” Himself in the act of procession and begetting. This is a single Being that is not moved, but simply finds source within himself; not source as in creation, but source as in existence. The Son has existence in the Father and the Spirit has existence in the Father.
Admittedly this is all a mystery and boggles the mind, but just because we cannot understand the Trinity does not mean the Trinity is not true. The fact is, the Trinity is at the center of who God is and we cannot understand his essence. This inability means that we can only be in awe when reflecting upon the Trinity.
Some might be tempted, in such confusion, to abandon the idea of the Trinity. By doing so, they create a God that can be comprehended to some degree by removing mystery. Likewise, they gain an easy explanation to how God is not subject to an infinite regress by “proceeding” or “begetting.” But in abandoning the Trinity, Christians create a bigger problem; they negate the idea that God is love.