Ancient writings are the witnesses because this is when the books were written. No one has problems with all the other ancient documents of the world such as Homer's Iliad and Odyssey. Yet there are far less manuscript evidence for those documents than the Bible. It's a matter of having faith that is based on fact or evidence or on your own opinions and preferences.
We have already covered that all religions cannot be equally credible because they disagree and I or you could simply make up our own.
These leaves us with which one. There is only one book that began with the inception of alphabetic writing and has been in continuous usage ever since. There is only one that has a such a large volume of fulfilled prophecies.

God has present testimony to His truth today each timeives are changed from selfishness to selflessness by Jesus Christ.