In believing Christianity is true, a Christian must reject all other worldview truth claims. That is because the nature of truth is that it automatically excludes that which isn't true. Therefore claims about how the world really functions, why it exists, and where it's going is a view of reality that can not be contradictory. To make the claim that it is so is a claim that is self-refuting. And a self-refuting claim can not be asserted.
Why bring all this up?
Well, modern day western Christians, often to accommodate worldly thinking because of the fear of man, often attempt to make their claims about truth, Jesus, the Bible, God, and sin a matter of personal opinion. Some even go as far as to say that these issues really don't matter, as long as you are sincere or a good person. Although this is clearly a works salvation, which doesn't save anyone, some Christians find solace with unbelievers when they make these claims.
The Bible must be believed, if you are to be saved. (I hear some moaning on that one.) Yes, I said it. You cannot be a true Christian, if you do not believe the Bible. Jesus, himself, said that there will be many who believe they are Christians, but are not disciples of Christ. This shouldn't be! (Matthew 7:21-27; Acts 11:25-26)
Objections from my own brothers
But you may say, "I believe parts of the Bible. Just not the miracles." My question would be, "On what basis do you believe that Jesus is the Son of God?" You also may say, "Well, I believe the words of Jesus, and that's all." My question would be, "Why is that? Much of what Jesus said maintained the veracity of the Old Testament passages. How can you assert the words of Jesus, yet reject what he claims to be true?" And for those who reject certain New Testament passages—because they are not colored red by modern-day printers—"Why do you accept passages that attest to the words of Jesus by those who attest the other New Testament passages that you reject?"
We have options
The problem is that there are mainly two alternatives opposed to careful acceptance of the Word of God. One is following what we think is right, and the other is following what we feel is right. The problem with the first is that what we think is right, may destroy us. (Proverbs 16:25; Proverbs 3:5-6) And the problem with the latter is that what we feel is right can deceive us. (Jeremiah 17:9)
The only real alternative is to follow Jesus and the apostles he gave for the task of showing us the Way.
Please. Don't be a fool.