How do we know the books of the Bible are accurate as originally inspired by God?

The Old Testament 

The Dead sea Scrolls- The entire Old Testament (except the book of Esther) was found in 1947 in a series of caves along the northwestern portion of the Dead Sea. The documents were placed in the caves by a sect of Jews known as the Essenes who placed  parchments in clay jars and hid them in the caves near the present-day ruins of Khirbet Qumran about 70 A.D. 

Many scrolls appear to have been written at least 200 years prior to their placement in the caves in 70 A.D. The documents remained hidden, protected and forgotten for nearly 2,000 years. When reclaimed in 1947, they were compared letter by letter to today's Hebrew Bible. The scrolls showed virtually no difference? This demonstrated that the Old Testament was passed down accurately. It's also apparent that the prophecies about Jesus Christ were made long before He arrived.

The Septuagint- is the Greek translation of the Hebrew Scriptures now known as the Old Testament. This version was transcribed between 250 to 200 B.C. This Greek translation was created from Hebrew over 200 years before Christ and some ancient manuscripts exist today. The content shows very clear consistency with today's Bible.

The New Testament 

The Manuscript Proliferation- Today we have over 24,000 early manuscript copies of portions of the New Testament. This vastly exceeds ancient works we consider "almost perfect" today. These include 
Plato, Aristophanes and the historical works by Julius Caesar and Herododus. Less than than 100 of these early manuscripts are known to exist. In addition all of these other ancient copies were written about 1,000 years after the event.

The books of the New Testament give an eyewitness description of what transpired within 25 years of the occurrences. These testimonies were transcribed after the ascension of Jesus into heaven but while His disciples were still alive.

The Manuscript Confirmation- The fact that many early manuscripts were easily confirmed by eyewitnesses is strong evidence of validity. After all, who would spend hours copying documents known to be false. The early persecution banned the Christian Bible. Anyone risking duplication would be murdered. There had to be a belief in content, after all it was historical fact, not mere philosophy.