This is the way it works. They seize on certain scriptures and apply them rigidly and literalistically. Everything is about the letter of these certain scriptures. Pretty much all pentecostal denominations are the same. But oneness takes it a step further, you must speak in tongues to be saved, or evidence you are saved. And, a very high standard of obedience is stressed. Everything revolves around the baptism in the Holy Spirit and speaking in tongues.
But there's a problem. Maybe its because of the zeal they have for what they centre around, that other things cannot be seen
I myself believe in what they term the baptism of the Holy Spirit, and I believe the Spirit leads us into truth. So it surprising to me, that many who stress tongues and the baptism so much, do not understand much about the gospel message those do who don't think like them do.
I asked two of them in this thread what is the new covenant, neither of them could tell me. I would be surprised if either of them knew the bible says the ten commandments are the letter that kills the ministry of death and condemnation. And I've never met any pentecostal who understood Paul's message of grace, neither have I heard it preached in any pentecostal church I've ever been in. In fact, when I was at a pentecostal church when I was young, I did not understand the message of justification/sanctification. I just grew up believing if I did not perform nigh on perfect I would be cast into hell. Of course, it would be unfair to tar every church the same, but by and large they would be
Charles Spurgeon probably did not believe as they do, but personally speaking, I've never read of anyone who so well expounds on Paul's message. He was known as the prince of preachers, but according to oneness he could never have been saved.
Zeal is good, but not if it blinds you to properly understanding the whole message. And salvific belief is very clearly spelt out in the bible, it is not only hinted at. Hence they are wrong