Q: What is "Oneness" Theology and why is it wrong?
A: Quite simply, Oneness theology teaches that God is one person who manifests himself differently — sometimes as God the Father, other times as God the Son and sometimes as the Holy Spirit. Oneness (also called modalism or Sabellianism) is known more commonly by the name “Jesus only” since adherents of this teaching usually believe the name of the One God is “Jesus.”
This teaching is traced back to the late 2nd and early 3rd centuries when two particular men, Praxeas and Sabellius, popularized and propagated this theological idea. Such teachings have always been considered aberrant and heretical by the Christian church at large and that is because Oneness teaching flies in the face of clear biblical revelation.
The Bible reveals that there is One God who is revealed within the pages of Scripture in Three Persons — Father, Son and Holy Spirit. Even in the opening pages of the Word we are privileged to overhear a conversation between these Three Persons at the time of Creation:
Then God said, “Let us make man in our image, after our likeness. And let them have dominion over the fish of the sea and over the birds of the heavens and over the livestock and over all the earth and over every creeping thing that creeps on the earth.” So God created man in his own image, in the image of God he created him; male and female he created them. Genesis 1:26–27 (ESV)
And, at the baptism of Jesus by John, we are shown all Three Persons of the Godhead at once, as the Son emerges from the water and Father’s voice is heard from heaven while the Spirit descends on the Son in the form of a dove. (See Mark 1:9–11; John 1:32-34)
A.W. Tozer writes:
Our sincerest effort to grasp the incomprehensible mystery of the Trinity must remain forever futile, and only by deepest reverence can it be saved from actual presumption. (Knowledge of the Holy)
(See also Matthew 28: 19; 1 Peter 1:2)