What is the ontological Trinity?

TL;DR:

The ontological Trinity of God is a formal way of describing what God is like. The ontological Trinity is important as it affirms the equality of the nature of each Person of the Godhead.

Ontology is a branch of philosophy which examines the fundamental nature of existence: the essential “being” of the subject. Applying ontology to God, as a Trinity, endeavors to describe what God is like in His most essential nature. The ontological Trinity is also sometimes referred to as the “immanent Trinity” or the “essential Trinity” and is frequently mentioned alongside the “economic Trinity.” While the ontological Trinity focuses on who God is, the economic Trinity focuses on God's actions, such as the role of the Godhead in creation, salvation, and sanctification. The Bible explains that each person of the Trinity—the Father, Son, and Holy Spirit—is equal in nature and qualities. Thus, all Persons of God share the same abilities, power, wisdom, strength, importance, and glory. This “ontological Trinity” is a part of standard doctrine within Christianity. It is crucial to Christian belief because it affirms the equality of the nature of each Person of the Godhead. Deuteronomy 6:4 says, "Hear, O Israel: The Lord our God, the Lord is one." Jesus affirms His oneness in nature with God, saying, “The Father and I are one” (John 10:30). Throughout the Gospels we see the uniform nature and coexistence of the Father, Son, and Holy Spirit (Matthew 28:19; Luke 3:21–22; John 1:1).

from the old testament

God is one (Deuteronomy 6:4).
God is depicted as a unified Trinity at creation (Genesis 1:1-2, 26-27).
God the Father gives authority to the Son to rule and reign as king (Psalm 2:7-12).
God the Father promises to put the Holy Spirit in His people (Ezekiel 36:26-27).

from the new testament

Jesus is one with God (John 10:30).
Triune God is unified at Creation (John 1:1-3).
God is unified at the baptism of Jesus and other believers (Matthew 3:16-17, 28:19).
Triune God resurrected Jesus (1 Thessalonians 1:10, John 10:17-18, Romans 8:11).
The grace, love and fellowship of God ministers to believers (2 Corinthians 13:14).
Triune God lives within us (Galatians 4:6).
Triune God has made Himself available to believers through Christ (Ephesians 2:18).

implications for today

Appreciation for the ontology of the Trinity is essential for the Christian seeking to understand the nature of God. The unique relationship of the Godhead, described in the Bible, communicates the unity of God which perfectly accomplishes His will. God seeks this type of unity with each of us as well. Even now, all three Persons of the ontological Trinity use their uniform nature to speak to us, reminding us that if we are in Christ, we are God's children: "And because we are His children, God has sent the Spirit of His Son into our hearts, prompting us to call out, “Abba, Father'" (Galatians 4:6). Jesus prayed for us to share in this special unity with God:

“I am praying not only for these disciples but also for all who will ever believe in me through their message. I pray that they will all be one, just as you and I are one—as you are in me, Father, and I am in you. And may they be in us so that the world will believe you sent me. I have given them the glory you gave me, so they may be one as we are one. I am in them and you are in me. May they experience such perfect unity that the world will know that you sent me and that you love them as much as you love me.”

–(John 17:20-23)

understand

The ontological Trinity asserts the unity of the three distinct Persons.
Each Person of the Trinity—Father, Son, and Holy Spirit—is equal in essence, affirming that there is no essential difference among them.
The ontological Trinity explains a different aspect of the Trinity than the "economic Trinity," for example, which refers to God's interactions and relationship with the world.

reflect

How does understanding the equality of the Father, Son, and Holy Spirit in the ontological Trinity deepen your relationship with God?
How can the unity of the Godhead influence your interactions and relationships with others in your life?
How can reflecting on the nature of the Trinity help you navigate feelings of loneliness or isolation?

engage

How do the concepts of the ontological Trinity and economic Trinity complement each other in our understanding of God's nature and actions?
How does the unity of the Trinity challenge or affirm our beliefs about authority and submission in our relationships?
What does the ontological Trinity reveal about God and how does that impact our relationship with Him?