How is it that such a fundamental concept of our faith as the Trinity is so poorly understood? Most Catholics do not really know the basic concepts of the doctrine of the Trinity. It is of paramount importance to our faith, and must be confidently held by all Catholics. Now the Trinity is indeed a very complicated subject and it is not humanly possible to fully comprehend its dynamics. It is possible, however to describe it in great detail and derive some benefit from this basic understanding. If it were of no importance to our faith, we would not have received this revelation from God.
The Trinity at first attempt is probably the most difficult component of our faith to grasp. There are three persons in one nature. The key here is to reject the mathematical approach that is normally the first route we take in examining this mystery. Three does not equal one, so we immediately can cease trying to make that connection. This excerpt from the classic book Theology and Sanity by Frank Sheed helps us understand the idea:
“There is no question of arithmetic involved. We are not saying three persons in one person, or three natures in one nature; we are saying three persons in one nature.” (p. 92)
First let us state clearly our understanding of the Trinity. There are three persons in one God: Father, Son, and Holy Spirit. Each of them is God, but there is one God, not three. Furthermore, each member of the Trinity is distinct from the other two persons, but not separate from them.
Now that we have a basic statement of the belief, we can begin to analyze it. By nature, we mean the essence of a thing. By person, we mean the entity which possesses the essence. Nature defines the set of actions a thing takes, while person is the thing that carries out the actions. The nature is the origin of our actions, while the person is the actor.
In humans, the nature is fully possessed and acted upon by one person. No other person has our individual nature. Indeed we all share a human nature, that defines actions every person can take, but we all possess an individual nature that differentiates our potentiality from every other person. God however has one infinite nature that is fully possessed and acted upon by the three persons in the Trinity.
We can reason that each member of the Trinity must be distinct, but not separate from the other members because they all share the one nature. If each member was separate, there would in fact be three natures, not one. There can only be one divine nature, since it is infinite in love, power, justice, mercy, and wisdom. If there was more than one divine nature, it would imply that each nature is capable of doing things the other nature could not do. This is a contradiction because to be infinite means to have no limitations.
To restate our description of the Trinity, we begin by admitting that we cannot fully understand all the dynamics of it, but we can describe it. Having asserted that, we do know that there are three persons in one God, three persons, each fully possessing the one diving nature.
For further reading on this subject, the following sources are invaluable:
Theology and Sanity – Frank Sheed
Catholic Encyclopedia article on the Trinity