Humans get to a truth by putting faith on a small amount of humans who are believed to be in direct contact with the truth itself. This is what human witnessing is.
Truths can be categorized as follows,
Type 1: Scientific truth
You can repeatedly and predictably verify the results by yourself. However, just like any other truths, a scientific truth is normally conveyed through human witnessing. Say, you don't observe the existence of black holes. You believe what is said by the scientists to get to such a truth. The scientists are a small amount of humans who are believed to be in direct contact with a scientific truth.
However, you can anytime verify the works of the scientists, because such a kind of truths is accessible all the times.
Type 2: Present Truth
They are the things/events happening around you or in this world. Such as daily news, the existence of Barrack Obama and so forth. Again, you don't examine them directly. You put your trust/faith to the media to get to such a kind of truths. Media is made up of a small amount of humans such as the writers and reporters.
Since the existence of such a kind of truths is in present time, they are thus accessible for your verification. You can examine the evidence by yourself.
Type 3: Historical Truth
They are the things/events happened in the past (possibly long past). Humans rely mostly on witnessing to reach such a kind of truth. For example, George Washington is believed to live between 1732 and 1799. We know this because there are humans records (possibly multiple accounts of them) saying so. Now what was Washington doing on a specific date, say, Feb 2nd of 1738? No one could possibly know because no one there wrote it down what he's doing on that day.
Mostly, history (= his story) is a result of human witnessing. The more distant history is, the less it is evidenced. Similarly, the less famous a person/an event is, the less was written down about him/it. Humans may thus find no way to reach such a truth.
History is mostly a one time event no longer accessible to today's humans. Humans will have to rely heavily and mostly on documents written by other humans to reach a truth. To put it another way, human witnessing can be the only way to reach a historical truth.
Type 4: Touchable Truth
This is the truth directly accessible to you. For example, water is wet. You can verify this by yourself at any time. You don't need to rely on others tales (witnessing) to know this. However, you may have to rely on witnessing to get to know deeper about what water is, say, at the atomic level.
Type 5: Unreachable Truth
They are truths not supposed to be reached by humans within a certain time frame. For example, humans living in stone age can hardly be aware of the existence of black holes. If somehow you are sent to the humans in stone age. Then they can reach such a truth by believing in your witnessing. If the existence of black holes concerns their lives, you can thus tell them: "I am the truth, the way and the live. Without me no one can reach the truth of black holes".
Similarly, humans living in our age may not access the existence of heaven, hell etc. even when they are real. To put it another way, even when they are real, such a truth can only be reached through human witnessing (which invites your faith to believe).
The truth of Christianity can be a mixture of Type 3 and Type 5 mentioned above. A truth requires witnessing to be reached. A witnessing invites faith to believe.
Today, we make use of multiple accounts, video and audio recordings to validate our witnessing (such as our daily news). Similarly, Bible is validated through multiple accounts. And no human witnessing can be made more valid than those direct witnesses martyred themselves for what is said and done.
Muslin is unsupported by multiple account witnessing, nor is it supported by the martyrdom of direct witnesses. It is because no humans and no gods ever understood the power of human witnessing. Only the Christian God can explicitly name His prophets and His witnesses. Only the Christian God asks for the conveying of truth through witnessing. Only the Christian God correctly makes use of human witnessing as a mean to convey a claimed truth.
Only God knows what witnessing is, no humans and no other gods can ever find out. Thus He can EXPLICITLY said,
Acts 1:8 (NIV)
But you will receive power when the Holy Spirit comes on you; and you will be my witnesses in Jerusalem, and in all Judea and Samaria, and to the ends of the earth.
Humans hear about witnessing all the times without actually understanding what it is. And God's summary about humans is correct,
Isaiah 6:9 (NIV)
Be ever hearing, but never understanding; be ever seeing, but never perceiving.
If any religion holds any truth, it is Christianity!
