Christianity is not a Belief System
I've noticed that there is a very common fallacy about Christianity held by many non-Christians (and even some professing Christians). I'm referring to the idea that Christians are those who hold a specific set of beliefs about God. That is incorrect. While certain beliefs about God are inherent to Christianity, it is about much more than that.
Reducing Christianity to a belief system is like saying marriage is nothing more than a set of beliefs about the opposite sex. Obviously, certain beliefs are required for a marriage. For example, if someone is married, it's pretty safe to assume they believe their spouse actually exists. However, someone could have all the right beliefs about the opposite sex, and still not be married. On the other hand, someone could really be married, but still have wrong beliefs. Marriage is a relationship, not a set of beliefs.
Similarly, biblical Christianity is a relationship. Christians claim to be in an actual relationship with God. The Creator of the universe literally lives with and in us. A person can have all the right beliefs about God and still not be in a relationship with him. The reverse is also true, someone could be in a genuine relationship with God and still have any number of wrong beliefs. (To be clear, I'm not saying that beliefs don't matter. They do, and there are often consequences to wrong beliefs. However, beliefs are not the defining attribute of true Christianity.)
Sometimes well-intentioned believers are guilty of perpetuating this misunderstanding when we tell people they just need to believe in Jesus to be saved. It is easy to see how this could be understood to mean merely intellectual assent to a creed. However, the Bible is clear that genuine salvation comes through repentance and trust in Jesus, and results in a transformed life. That's much more than a belief system.