Because the Christian vision of God is unique, mysterious, and inscrutable to the finite mind, it is often misunderstood and misrepresented. Let’s briefly examine what the doctrine of the Trinity does and does not teach by underscoring three points.
First, there exists only one God (one divine essence or being). Trinitarianism is a unique type of monotheism, and the underlying truth of monotheism is grounded in the Old and New Testament Scriptures (Deuteronomy 6:4; 1 Timothy 2:5). Orthodox Trinitarianism therefore rejects polytheism (many gods) in general and tritheism (three separate gods) in particular, for they divide the one divine essence.
Second, the three persons of the Godhead are each fully and completely divine, all sharing equally and totally the one divine essence. The deity of these three persons is also grounded in the Old and New Testament Scriptures (Father: 2 Peter 1:17; Son: John 20:28; Holy Spirit: Acts 5:3-4).
Third, the three persons of the Trinity should not be understood as three “parts” or “fractions” of God. Each person is fully divine and equally possesses all of God’s being. And, the term “person” in reference to the Trinity is used in a unique sense and should not be understood to refer to a separate entity or being, for this would divide the divine essence.
Unlike all finite creatures, God possesses plurality of personhood within His one infinite being. As the ancient Athanasian Creed proclaims:
We worship one God in trinity and the trinity in unity, neither blending their persons nor dividing their essence.
For more on the historic Christian doctrine of the Trinity, see “How Can God Be Three and One?” in my book Without a Doubt: Answering the 20 Toughest Faith Questions.