Mystery of the Trinity Part 2

Part 2: Essence, Nature, and Person

To understand the Trinity, we must begin by using the right words carefully. The Church teaches that God is one in essence, one in nature, but three in persons. That claim is not meaningless—it’s rooted in precise metaphysical language that distinguishes what something is from who it is.

These terms—essence, nature, substance, and person—are not word games. They help us speak about a reality that goes beyond sense experience without falling into contradiction or confusion. In this part, we clarify these distinctions and explain why they matter for Trinitarian theology.

Essence, Nature, and Substance

Essence

The essence of a thing is what it is—what makes it to be that kind of thing and not another. The essence of a triangle is to be a three-sided figure. The essence of a man is to be a rational animal. When we ask, “What is it?”, we are asking about essence.

Nature

Closely related to essence is nature. Nature is the essence of a thing considered in its activity. It answers the question, “What kind of action does this being perform?” A human nature acts rationally and freely. A horse acts instinctively. Nature tells us how a thing operates according to what it is.

In God, essence and nature are the same, because God is pure act—there is no potentiality or difference between being and doing.

Substance

Substance is what exists in itself and is the subject of properties or accidents. A person is a substance because they exist on their own, not in another. My individual humanity is a substance. My height or weight are accidental qualities. They can change without changing what I am.

In God, there are no accidents. God's essence and existence are the same. His nature is not something He possesses—it is what He is.

So when we speak of the one divine substance, we mean the one self-subsisting, necessary being who is not made of parts and has no distinction between what He is and that He is.

What Is a Person?

This brings us to the key term for Trinitarian theology: person.

Following Boethius, the Church defines a person as “an individual substance of a rational nature.” A person is a “who,” not a “what.” A person is a subject who knows, wills, and acts. We do not say a rock is a person, because it cannot reason. We say a man or an angel is a person, because they have intellect and will.

In the Trinity, we speak of three divine persons. These are not three substances. There is only one substance—one divine essence. But within that one substance, there are three distinct relations that each subsist as a person.

Why Person Is Not the Same as Essence

This distinction between person and essence is absolutely essential.

• Essence refers to what something is.

• Person refers to who it is.

In the created world, every person has their own nature. I have my humanity, and you have yours. But in God, there is one nature shared by three persons. The persons are not three examples of the divine nature. They are each fully God, because they each are the one divine nature.

How can that be? Because the persons are not distinguished by what they are, but by how they relate. The Father is unbegotten. The Son is begotten of the Father. The Holy Spirit proceeds from the Father and the Son. These are real distinctions—but not distinctions of essence or power or being. They are relations of origin.

Why This Matters

This is more than vocabulary. Without these distinctions, we fall into serious errors:

• If we say the persons are just roles or appearances, we fall into modalism (one person playing three parts).

• If we say the persons are three beings, we fall into tritheism.

• If we confuse person and nature, we cannot explain the Incarnation or the Eucharist.

These metaphysical tools allow us to preserve what the faith confesses: one God, three persons, without division or confusion.

Looking Ahead

Now that we have clarified what we mean by essence and person, we are ready to consider the inner life of God. In the next part, we will explore how the divine persons are distinguished by processions—not physical or temporal movements, but eternal acts of knowledge and love within the one, simple God.

“O eternal Trinity, you are a deep sea: the more I enter you, the more I discover, and the more I discover, the more I seek you.”—St. Catherine of Siena