Question: From where does the idea that Christianity the only **true** religion come? Other religions claim the same. What is the basis for the Christian claim?

Answer: 
**At one level, this question is easily answerable.** 

Christianity is based upon the idea that Jesus is who He claimed to be. And He said, in John 14:6 

> 
> I am the way and the truth and the life. No one comes to the Father
>  except through me.
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> 

And if Jesus is who He claimed to be, then Christianity must be the only true religion, because He said *specifically* "No one comes to the Father except through me".

**At another level, there are other answers, but too large to fit in a single answer here.**

If you're looking for external evidence, there's an entire field of study, known as [Apologetics](http://carm.org/apologetics) that seeks to provide a defense for the veracity of Christianity, its teachings, the identity of God, and the Truth of the Bible. 

There are volumes of information available (as well as counter-points arguing against the Truth of Christianity). Put simply, there's much too much information to make your question answerable in this forum. A Google search for "Apologetics," however, is a good place to start.
Ravi Zacharias has to say following on this question. From one of [his video talk](http://jesusonline.com/pvideo-how-do-you-know-that-christianity-is-the-one-true-worldview-ravi-zacharias/?utm_source=Y-Jesus&utm_campaign=e17e96b94f-Y_Jesus_Newsletter_02_10_2014&utm_medium=email&utm_term=0_facce9096f-e17e96b94f-301433262#.Uv8wJWKSxHS), here is the transcript:

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> ...Take a look at other world religion and see how these four question are dealt with: Origin, meaning, morality and destiny. These four questions are to be answered in two ways. Every particular answer has to correspond to truth, either through empirical form of measurement or through the logical reasoning process and when those four answers are put together they must cohere and not be incoherent. So the two tests should be correspondence and coherence. Only in Judaeo-Christian worldview will you find these four questions answered with corresponding truthfulness and with a coherence of world view.
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> In the Koran, it is the only historically claimed document that denied Jesus Christ was actually crucified and died on the cross. It denies it. The Greek historians say that he died on the cross, Roman historians say that, Pagan historians says that, Jewish historians says that and Christians historians says that. So historically it is making an affirmation that is really historically untrue.
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> Origin, meaning, morality and destiny: the Judea-Christian view is not the only one to claim exclusivity but is the only one that takes those four questions with corresponding answers that are truthful and coherent answers that stands the test of time. And the ultimate answer:The resurrection of the dead, that gives you the hope and meaning....
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