Is the issue regarding Oneness versus the Trinity more of a semantic debate over terms and precise theological definitions rather than a salvation issue?
That is an important question. One must say that a shocking number of people in the pew do not know their own doctrinal belief or at least know it well. It is fascinating that when you begin to teach Bible studies with many of the average Trinitarians, when you begin to talk to them, you discover they are functionally Oneness. However, that does not mean our understanding of the Godhead is a small issue. It is, in fact, critical to salvation.
How is the Oneness of God critical to salvation? Jesus said it this way, “I said therefore unto you, that ye shall die in your sins; if you do not believe that I am he, you will indeed die in your sins” (John 8:24). While this reference has been disputed in interpretation, any approach leaves the unbeliever in trouble.
“I am” (ego eimi) is the Greek equivalent of the Hebrew words found in Exod. 3:14 and Isa. 43:10. So “I am that I am” compared with Jesus’ statement would show that He is none other than the one God of the OT. Further, Jesus would be claiming that belief in Him as the one God or “I am” (singular here) is essential to salvation.
The other way this verse is compatible with Oneness is to say Jesus is speaking in His role as the Messiah, the Christ. Jesus would be telling the people unless they accept Him as Messiah they are going to be lost. Why would acceptance of Him in this role as man be essential to salvation?
Scripture makes it clear that sin alienated us from God. God came to save us in the person of Christ. That means Jesus is our only lamb, sacrifice, High Priest, mediator, etc. The man Jesus is our only “way to the Father,” the “one mediator between God and men,” so if we reject this only means of salvation we will be lost. Why?
Here is the crux of the matter. The false doctrine of the trinity affects salvation because people are baptized into a trinity instead of the one and ONLY saving name: Jesus (Acts 4:12). It is Jesus the man who died for our sin (Isa. 53). What’s fascinating is at this point in books and sermons, most Trinitarians discard speaking of the trinity subconsciously and begin to speak of the work of the man Jesus. They quote verses like 1 Timothy 3:16 talking about how Christ was taken to heaven in glory. But what glory? This is disclosed in Phil. 2:10, 11. “Every knee shall bow and every tongue confess that Jesus Christ is Lord to the glory of God the Father.” Why not the trinity? Because it’s not about persons, but the work of the man accomplishing the will and plan of God which brings salvation to fulfillment: namely by being the lamb that was slain from the foundation of the world.
Either way we look at this particular verse, we must be clear. Oneness is essential to understand because of the necessary mediatorial role of the man Jesus in our salvation. Baptism in Jesus’ name isn’t just a way to define ourselves against our Trinitarian friends. It’s application of the ONLY saving name.