updated 2020 October 17th
I'm an Apostolic Pentecostal Christian and I believe in the Oneness view of the Godhead. We believe that God is one. We do not believe that God is 3 in 1. We believe it is the same God who is the Father, Son, and Holy Spirit. His name is Jesus.
I used to be Trinitarian. The doctrine of the Trinity believes that God is 3 distinct yet inseparable gods or divine "persons" in the Godhead: The Father, the Son, and the Holy Spirit. It's been compared to a 3 leaf clover. The Son's name is Jesus.
I do want to say that I believe Trinitarians and Oneness Christians are both genuinely Christian and we have the same God. We simply have different views of the Godhead and how God can be the Father and the Son and the Holy Spirit.
I had never heard of the Oneness view until I met an Apostolic Pentecostal friend in 2011. The Trinity had never really made sense to me. I accepted it as a great mystery that I couldn't fully understand. When I first heard of Oneness I was leery having had been taught that any church not adhering to the Trinitarian view was not really a Christian church or at least not an acceptable denomination. I was intrigued. As I studied, I found myself unable to prove them wrong. I found the Trinity, however, to not be as bible-based as I thought it was.
Consider these things.
God . . .
The prince of peace, the eternal father, the king
revealed in the flesh (1 Timothy 3:16)
the image of the invisible God (Colossians 1:15, 2 Corinthians 4:4)
an exact representation of His nature (Hebrews 1:3)
radiance of His glory (Hebrews 1:3)
the fullness of the Deity in bodily form (Colossians 2:9)
I see one God in the bible.
A couple other verses to consider:
How can God be the Father and the Son and the Holy Spirit?
God is omnipresent. He is everywhere all the time. He can be in numerous places at once; he can be in heaven and in spirit form and in bodily form all at the same time. He is that powerful. He is that big. He has no limits. He is not restricted the way that mankind is. He is able to manifest himself in multiple ways. He is not divided or weakened. He is one.
A man can be a couple's child, a woman's husband, and a child's father all at the same time. One man can be in those 3 roles without being divided. Surely God can be in 3 roles without division or restriction.
The doctrine of the Trinity became accepted in 381AD at the First Council of Constantiple. The apostles didn't teach it. The early church didn't teach it. Jesus didn't teach it. The bible does not use the word Trinity nor does it say anything about "God the Father, God the Son, and God the Holy Spirit" with a triune teaching. The Trinity is using man's logic to explain how God can be in 3 roles. It is not in scripture nor is it a direct interpretation of scripture. Coming to that revelation and studying the scriptures above was sufficient for me to stop following the trinitiarian view.
God said in his word that he is one. Jesus said he has come in his father's name and the holy spirit will be sent in his name. The bible says Jesus is the image and representation of God revealed in the flesh (bodily form). The bible says that the fullness of God was in him. I believe it. I believe that God is One. Jesus is God. This is what I follow.