Updated: Nov 13, 2020
Members of the LDS church have been claiming to be the true Christian faith system, for generations. When someone disagrees, it's taken personally. It's as if "not Christian" is equated with "not Christ like". Let me be clear, an individual can serve society well, be charitable and compassionate, and still deny the very foundations of faith prescribed in the Bible. Mormonism is a perfect example of this. The community I grew up in was tight knit. We took care of our own. I can't say how many times members of the LDS church brought us meals, donated clothes when the school year began, or offered me babysitting gigs.
This post is not about the moral successes or failures of the LDS church. It's about the foundation of belief and how it differs from Christianity.
I'm not going to waste time talking about the different definitions of biblical words, such as "grace" or "salvation" or "repentance". The fundamental difference between Christianity and Mormonism, can be summed up in the concept of eternal progression. This is the idea that we are all progressing toward becoming gods. The 5th President of the LDS church, Lorenzo Snow, said the following, “As man now is, God once was; as God now is, man may be” https://www.churchofjesuschrist.org/study/ensign/1982/02/i-have-a-question/is-president-snows-statement-as-man-now-is-god-once-was-as-god-now-is-man-may-be-accepted-as-official-doctrine?lang=eng. To Christians, who are monotheistic (Isaiah 44:6), this is blasphemy.
Throughout the Bible, God describes Himself as the beginning and end (Revelation 22:13); as completely different from mankind (Isaiah 55:8-9); as jealous for the devotion of creation (Deuteronomy 4:24). Eternal progression is not compatible with monotheism. It's that simple. Monotheism is a core belief of Christianity (and its parent, Judaism). If you change that, is it even the same faith? When people say Mormonism isn't Christian, it isn't a personal judgement on the state of someone's heart. It's a statement made from logically comparing the two belief systems, and realizing they are fundamentally different.
Which faith system is right? Well, that's something we each decide on our own. What I'm trying to point out, is you can't group them together as the same thing. Mormonism is exclusive in its teachings and principles. That's why a baptism in a Lutheran or Methodist setting, doesn't count in the Mormon church. You have to be re-baptized when you accept Mormonism. You can't simultaneously demand acceptance and give rejection. The claim that the LDS church is "the one true church", assumes that all other churches are false. If they are false, why would the Mormon church want to be grouped in with them? It's a bit hypocritical to claim exclusivity in salvation, and then be offended when others do the exact same thing.
There are many other differences between Christianity and Mormonism. But this is the most significant, at least in my mind. The definition of who God is, is at the center of differentiating between faith systems. That's as true outside of this conversation, as it is within it. Who/what we put our faith in matters. If it didn't, why would we even have different religions? The fact that there are an array of different faith systems, suggests that people care about who/what we worship. If we want to have a meaningful discussion about who is right or wrong, we need to be honest about these differences.