I have just read a staggering article by a leading "evangelical" on the question of Mormonism and whether Mormons are Christians (article here).
Richard J. Mouw says the question, "Are Mormons Christians?" is a complicated one. I honestly don't know what can be complicated about it! It is evident that if one group believes in one eternal triune God, believes that salvation is through faith in Christ alone, and believes the Bible is complete, sufficient and contains the faith once for all delivered to the saints, and another group believes in an infinite regression of gods, none of whom is eternally God, all of whom were once men, and they believe in salvation by works, and they believe in subsequent revelations which contradict the Bible, these two groups are not the same!
Now it's not as if these differences are trifling disagreements on peripheral issues - the nature of God and the way of salvation are about as fundamental and foundational as you can get, and Christians and Mormons believe completely different things! Joseph Smith recognised this when he described the beliefs of Christians in his day as an abomination.
What is a Christian, and how do you become one? Well look at how Paul sought to persuade Agrippa to become a Christian (Acts 26). A Christian is one who has received forgiveness of sins, and has been brought to God, and has been given an inheritance, through faith in Christ (v18). That is the condition - faith alone in Christ alone. If you have a Christ who is not eternally divine you have one who cannot save. If you are not trusting alone in the almighty, eternal Son of God, He will not save you.
The differences are massive, it's not complicated.
