Its common argument that I have seen when I have asked Christians why they believe they are on right path and others are wrong. Certainly every religion claims to be truth. People try to say something like "which religion god died for your sins"? Only in Christianity so its the truth. Well that's no proof/reason to believe Christianity is truth. The doctrine itself is no proof its the truth but it must be something different. Please try not to answer similarly but provide strong argument because all scriptures have their doctrines and that itself is no proof.