I believe the only view of the Godhead that is consistent with the entire Bible is the Trinitarian view. One God in three persons (Hebrews 1:3 refers to God as a person).
Since I believe in one God I do not like to use the term “Oneness” when referring to “Oneness Pentecostals” but rather modalism.
They believe in one God in three modes rather than one God in three persons. They believe Jesus is the Father in a different mode, the Son is the Father in a different mode, etc.
Trinitarians believe Jesus is not the Father and the Father is not Jesus but both are fully God.
Modalists believe Jesus eternally existed with the Father as nothing more than a thought or a concept when Jesus said He was with the Father before the world was (John 17:5, John 1:1-2).
Phillipians 2:5-8 states Jesus existed with and was equal to the Father before His incarnation.
The Bible records discussions between the Father and the Son before He came to earth as God incarnate (Hebrews 1:5-8) and the Father calls the Son God and states the Son has a throne.
Here are a few passages that clearly refute modalism heresy:
John 8:16- 18: And yet if I judge my judgment is true: for I AM NOT ALONE, BUT I AND THE FATHER THAT SENT ME.
It is also written in your law that the TESTIMONY OF TWO MEN IS TRUE.
I AM ONE THAT BEAR WITNESS OF MYSELF, AND THE FATHER THAT SENT ME BEARETH WITNESS OF ME.
The above is referring to the testimony of two witnesses and referring to the witness of the Father and the Son.
Hebrews 6:16-18: For men verily swear by the greater: and an oath for confirmation is to them an end of all strife.
Wherein God, willing more abundantly to shew unto the heirs of promise the immutability of HIs counsel, confirmed it by an oath:
That by TWO IMMUTABLE THINGS, in which it was impossible for God to lie, we might have a strong consolation, who have fled for refuge to lay hold upon the hope set before us:
The passage above shows God making a covenant with Himself (Hebrews 6:13). The two immutable things are the Father making a covenant with the Son (Hebrews 7).
Hebrews 7:17- For He testifieth, Thou art a priest forever after the order of Melchizidec.
Hebrews 7:22- By so much was Jesus made a surety of a better testament.
God the Father making a covenant with God the Son, swearing by Himself is the two immutable things by which is it impossible for God to lie.
John 17:21- That they all may be ONE: as thou, Father art in Me and I in Thee, that they also may be one in us:
Here in John 17 Jesus is praying for believers to have the same unity and agreement that He and the Father have together.
He is not praying for believers to become the same literal person.
For modalist doctrine to be consistent to it’s teachings you would have to twist this prayer of Jesus in John 17 to mean Jesus was praying for believers to become literally the same person.
John 8:29- And HE that sent ME IS WITH ME: THE FATHER hath not left ME ALONE; for I do always those things that please HIM.
John 14:23- If a man love ME he will keep MY WORDS: AND MY FATHER will love him, and WE will come unto him and make OUR abode with him.
John 17:5- And now O FATHER, GLORIFY THOU ME WITH THINE OWN SELF WITH THE GLORY WHICH I HAD WITH THEE BEFORE THE WORLD WAS.