If you believe in Christ but reject His unique deity, you might have a very nice religion, but can you call it Christianity?
Must a person believe that Christ is God in order to be saved? I don't think it is necessary for you to be aware of that doctrine and hold to it before you can become a Christian and receive forgiveness. But I think that you have to know some doctrine in order to be a Christian, in order to receive God's gift of salvation. I think it is a very fundamental and basic doctrine that you need to know. Basically, you need to know your need and God's provision in Jesus, and then respond to that by trusting Jesus for your salvation. In other words, you trust in the person of Jesus Christ. It may be after that that you find out that Jesus is also God. You don't need to know that Jesus is God before the fact.
In fact, I don't think that the early church had a precise view of that like we do now. I think some of the details of this were worked out in the history of the church during the first couple of centuries. I think it's all there inherent in the Scriptures. I think the early church believed in the divinity of Christ but wasn't sure what to make of that. They weren't sure exactly how all that worked out, and they didn't bother themselves with it because their job at that point wasn't to refine their theology; it was first of all, to get the basic Gospel out and, secondly, to stay alive. So it wasn't till later that they refined these things.
I don't think that a person can repudiate the deity of Christ and call themselves a Christian because I think that the notion of the deity of Christ--God becoming man, God in three persons, one essence--is an essential defining doctrine of the faith. In other words, if you reject an essential or defining doctrine then you cannot call yourself by the title that is defined by these doctrines.
Every word has a definition and usually the definition entails a couple of different things that make the full definition, and if the details are not there, you can't apply the word. The same is true of "Christian." The word Christian and being a Christian entails a couple of particular things historically. One of those particular things is that you believe in the unique deity of Jesus Christ--the Trinity, God become man, Jesus Christ being fully God and fully man, two natures, one person. If you reject that, you might have a very nice religion, but you just don't have Christianity. So in that sense you can't be a Christian and reject the deity of Christ.
Part of the reason I would say that is that we are to believe in God and in Jesus Christ as He is in Himself. In other words, it doesn't seem to me that you can deny the nature of God, the nature of the God of the Scripture, and still call yourself a Christian. John says in John 4:24, "God is spirit, and those who worship Him must worship in spirit and in truth." In other words, there are some fundamental things you have got to have right about God or at least not be willing to repudiate. You can learn them, but once you repudiate them you are repudiating the very God you are saying you are seeking to worship. This is a God who is one God in essence and in substance, but has three persons, Father, Son and the Spirit; and the second person, called the Logos in John 1, takes on humanity, becomes a real man such that Jesus Christ is one person with two natures--the full nature of divinity and the full nature of humanity. And if you reject such a thing, I don't see how you can then say I have put my faith in Jesus because the Jesus that you put your faith in is not the Jesus of the Scriptures, and it is only the Jesus of the Scriptures who really saves you.
So I think that it's actually very critical and I think it's important to point out that Paul himself talked about another Jesus that was preached that some unfortunately accept, but a Jesus that is contrary to the Jesus of Scriptures. In fact, Jesus warned in Matthew 24 that one characteristic of the end times is the fact that false messiahs would come and claim to be someone special and mislead many. And I think that false messiahs are individuals who claim to be messiah or else substitute definitions for the Jesus of Scripture. I think the denial of the deity of Christ is such a substitution.
The Scripture teaches clearly not only that any old god won't do--and we see that in statements like Exodus 20:2-3, "I am the Lord your God who brought you out of the land of Egypt, out of the house of slavery. You shall have no other gods before me." The first commandment in fact. We must have the correct God before us. By the same token, any old Jesus won't do either. Jesus says in John 8:24, "Unless you believe that I Am, you shall die in your sins." According to Jesus it was very critical that we have a particular belief about him, and if we don't then we are lost in our sins.
It isn't enough to simply believe in Him. And by the way, that text in John 8 is when Jesus was addressing particular people who had believed in Him in some fashion. But one needs to have an accurate belief in Jesus, not just any belief in Jesus in order for the true Christ to be their savior. I think that those are very critical distinctions and we have to hold to those if the word Christian is going to continue to mean something in particular and not just any religious thought that has to do with some man or any man named Jesus.