Question:
Islam says that if you cannot find your answer in the Quran, turn to the saying of the Prophet (PBUH) in the Hadith.  If you cannot find the answer there, turn to the Old and New Testaments.  But at the end of the New Testament, it says this is the only book and you shouldn't follow any other book. "Why?  Why does Christianity not leave room for other religions to co-exist?"  This is one stereotype I grew up with.

Answer:
My dear friend, You have asked a great question. I can understand why this comes to your mind.

There are a couple of preliminary questions that need to be raised. The first is this: Is there such a thing as absolute truth? Many in our world would answer no. And if there is no absolute truth then Christianity or Islam or believing in aliens might be nice philosophies and "true" or helpful for individuals, but they wouldn't be truth. The second question is: Has God spoken to mankind? Again, if the answer is no, then every religion is pretty much equal. Everyone would be guessing what God is like but no one could know for sure.

Christianity and Islam however say there is absolute truth. That means that something may be true whether someone believes it or not, or likes it or not. The tree is green whether I believe it or not, it is objective truth. Christianity also proclaims the fact that God has intervened in this world and has communicated to this world. He has revealed himself to us. He has revealed the truth.

So how does this apply to other religions? Jesus said, "Enter through the narrow gate. For wide is the gate and broad is the road that leads to destruction, and many enter through it. But small is the gate and narrow the road that leads to life, and only a few find it." (Matthew 7:13-14) Here Jesus makes the point that there is a way to God. It isn't that all roads lead to the same place. There is one road that leads to God and sadly only a few find it. Jesus was even more specific when he said, "I am the way and the truth and the life. No one comes to the Father except through me. If you really knew me, you would know my Father as well." (John 14:6-7) Jesus was saying that he was the way to God. All other roads lead away from God.

For this reason, the Bible says that any other message is not from God but from the mind of man. And why this is important from a Biblical perspective is because it all goes back to the way of salvation. If Jesus is the way, then to miss that way leads to destruction. If he is only one way, then there is no problem and any religion will do. But that is not what the Bible teaches and that is why Christianity says other religions are in error.

Christians therefore are commanded by God to proclaim the truth. However Christians are not allowed to use force or mistreat a person of any other religion. God doesn't even force people to believe in him. In Isaiah God is speaking about his people and said, "All day long I have held out my hands to an obstinate people, who walk in ways not good, pursuing their own imaginations." (Isaiah 65:2) He was there, he wanted them to have a relationship with him, he wanted to bless them and show them the extent of his love but they were obstinate. In the same way Christians who want to follow the Bible seriously will try to speak the truth in love and respect. And whether a person listens or not the Christian is to love that person. And what is more, the Christian will allow that person to worship or believe as he has decided.