I'm not defending the oneness Pentecostal doctrine. However, I've known some of them with exemplary walks with God: an appreciation of their own sinfulness and reliance on the substitutionary atonement as their only hope of salvation. Their understanding of the trinity is different, that there is one person with three manifestations. In my humble opinion it is only by putting undue emphasis on confessions, moving away from sola scriptura, that one can make the Reformed view of the trinity into the shibboleth of salvation.
The theology of a person does not need to be perfect in order for him to be saved. It may even be (and I have seen this) that someone who has deficient theology would have a closer walk with the Lord than someone whose theology is "better."
But you are talking about a central issue. A true Oneness Pentecostal cannot rely on "
the substitutionary atonement as their only hope of salvation." Why? Because a Oneness Pentecostal cannot believe in Jesus Christ as the Son of God, the Second Person of the Trinity- God who
became man to die on a cross for his sins. The Oneness Jesus is a facade; he is God pretending to be another person (since he is not) taking on a role (hence the term "Modalism."). This has absolutely nothing to do with "Confessions." This is not a "Reformed" view. It is not just an Arminian view. It is a Roman Catholic view. It is an Eastern Orthodox view. It is the view of every branch of the visible church.
The Oneness Pentecostal denies the truth of Scripture that God is One and yet is Three. He must of necessity deny the "God sent His son" because they are the same person. He must deny Christ praying to His Father in John 17, because they
are the same person to him. He must deny that Christ offered himself through the eternal Spirit,
because they are the same person to him. Almost every truth about God in the NT is a lie for the Oneness Pentecostal. The Oneness Pentecostal's view of God is deficient even when compared to an NT era Jew's, and we see what our Lord thought about him.
A Christian
must be Trinitarian. This has always been the case: from the Apostle's Creed, to Peter's sermons in Acts. There cannot be the slightest compromise on this, for it makes my Jesus a cruel mocking joke. He is not God, nor the Son of God, according to the Oneness Pentecostal. He is a play being put on by a lying God. That is simply unacceptable.