I have a family member who, many years ago, left the Catholic faith and joined a Oneness Pentecostal congregation. I recently visited her and spent many hours (in a conversation she initiated), listening to her attack the doctrine of the Trinity as a 3rd Century innovation as well as attacking the Trinitarian Baptismal formula, infant baptism, and baptism by pouring.
I cited the fact that when Jesus prayed in the garden, He asked for thy (the Father’s) will be done, not His (the Son’s). I asked how one person could have two distinct wills. I also pointed out that Jesus said he would send another paraclete (the Holy Spirit). I also mentioned the baptism of Jesus, and John 1.
As for the baptismal formula, her argument is that (according to the notes in the New Jerusalem Bible) the formula used in Matthew 28 was likely modified from the original oral tradition based on the development of Trinitarian doctrine. She supports this by pointing out that every example of Baptism in Acts is “in the name of the Lord Jesus Christ.” My explanation of this is that the phrase “in the name of the Lord Jesus Christ” is to identify on whose authority, and under whose directions the Baptisms were being performed, not to describe the specific ritual.
Of course I was not telling her anything she had not heard before and she insisted that the doctrine of the Trinity was not formulated until the 3rd Century and that her belief in One God who is not Triune is the “Apostolic” view.
I ask two things. First and foremost, pray that she may be brought back from her apostacy and recognize the Triune nature of our God. Second, if anyone has any compelling points, of course relying on scripture alone, since that is the authority she recognizes, that demonstrate the Trinitarian nature of the Godhead, please respond with these.