Ok, then can you please elaborate on your statements and questions?
Muslims don't have an authenticity problem? They claim the Qur'an is the literal word of God where he bounces back and forth mindlessly from third person to first person and constantly contradicts himself and makes ridiculous claims (and backs nothing up). It was written hundreds of years after anything in the Bible. They have a much bigger validity problem than ANY religion because they have the nerve to claim that if even one error or contradiction is found, then nothing in the book is from God. Christians make no such claim, although our book is significantly more consistent and cohesive.
Jews are in the same boat as Christians, for the most part. The Bible has stronger manuscript evidence than any piece of classical literature. You can be more certain that the Bible is authentic than you can something like... Plato or Homer. There was a shorter time lapse between actual events, written documents and subsequent copies than with any other writing. The Iliad, for example, only has 643 manuscripts with a 500 year span between copies (and those events never really happened). The New Testament, on the other hand, has more than 24,000 manuscript copies with a time span of only 25 years between copies and originals. There are only 40 lines of doubt across all 24,000 manuscript copies of the New Testament. There are 746 lines of doubt across 643 copies of the Iliad.
The New Testament is full of witness testimonies, hence the names of the books. You should read it some time and this will make more sense.