Wow can we be sure the ancient biblical manuscripts are from the originals and that these manuscripts are what the current Bible is based up?
Mountains of Manuscripts
If we say that there is a “mountain of evidence” in biblical manuscripts, we would not be exaggerating. The enormous amounts of ancient biblical manuscripts and copies of manuscripts make the Bible the most authenticated book in human history. To begin with, in an old Jewish synagogue in Cairo, Egypt, they discovered more than 260,000 Hebrew manuscripts, of which 10,000 are biblical manuscripts. Then, there are more than 200 biblical manuscripts among the Dead Sea Scrolls, and all of which were written before the year 70 AD, so altogether, there are well over 5,600 ancient biblical manuscripts from the Old Testament, including works from several different authors. Most of these authors had never met, yet their doctrinal recordings are the same as with the other authors, and they’re consistent with the other Old Testament and New Testament authors, so these manuscripts are amazingly accurate. All of these are textually in agreement with each other, with the percentage of copying differences at about .01%, however, these differences are only because of vowel differentiation, and consonant blends, but they do not affect the text or the context. The earliest book of the Bible we have is thought to be the Book of Job, written even before the Book of Genesis. That’s because Job mentions contemporaries of Abraham and other biblical figures in ancient times, even before Israel was a nation. Job was the son of Zare who was one of the sons of Esau, so Job was from the fifth generation after Abram (Abraham). 
The New Testament has been preserved in more manuscripts than any other ancient work of literature, with over 5,800 complete or fragmented Greek manuscripts that have been catalogued. There are 10,000 Latin manuscripts and 9,300 manuscripts in various other ancient languages including Syriac, Slavic, Gothic, Ethiopic, Coptic and Armenian, so the New Testament manuscripts have been preserved by the thousands, and these copies found in different parts of the world are still consistent with each other. If you were to take any other ancient work of antiquity or even a fairly recent historical book, not one of them would compare to the mountainous volume of supporting manuscripts and various fragments. There is absolutely no other ancient work or book in human history that has the documented support that the Bible has. And the biblical manuscripts continue to pile up as I write this, and when we realize just how close these manuscripts were written within the lifetime of the New Testament authors, it’s clear to see that they must be the Word of God. The New Testament manuscripts range from the 2nd century up to the invention of the printing press in the 15th century, and it seems that every few years, 2 or 3 handwritten copies or manuscripts of the New Testament arrive, many of which are in the original Greek. One of the largest discoveries was in 2008 when 47 new manuscripts were discovered in Albania, and at the time of discovery, at least 17 of them were unknown to Western scholars.
Who Wrote the Bible?
Was the Bible written by man or by God Himself? Many believe it was written by man and thus they claim they cannot believe it, but if it was written by man, then it could contain human prejudices and errors. If it is written by God, then we would expect it to be perfect, so does the Bible claim that the Word of God is actually the very words of God? According to the Bible, there are 418 times that the Bible uses the term, “Thus says the Lord,” and then there are another 48 (that I could count) that says “God said,” so if you add up all of the “Jesus said” and the other accounts of God telling the 40 authors in 66 books that God told them to “write down” these words, then the Bible contains well over 1,000 references where it says that the Lord was speaking or caused the words to be written down by His Spirit. Some cults take out or add to the Word of God, and some even have their own translations (i.e. the New World Translation), but there is a serious warning to anyone that distorts, twists, adds to, or takes away from Scripture. God declares that if any human adds to or takes away from the Word of God, even a single letter or stroke, that He “…shall take away his part out of the book of life, and out of the holy city (heaven or the new Jerusalem)” (Rev 22:19). This warning is repeated in Deuteronomy 4:2 where it states, “You shall not add to the word that I command you, nor take from it, that you may keep the commandments of the Lord your God that I command you.” There is not a single instance where it says that men’s words were written down as Scripture, but rather, it says, “Thus says the Lord” (Jer 9:23a), so it is the Lord God Himself Who speaks through Scripture and not man.
To say that men wrote the Bible and all of the ancient manuscripts would be like saying my keyboard wrote this article when it was actually me that wrote it. I was the instrument that moved the keyboard to record what I wanted to write and not what the keyboard wanted to write. The keyboard is powerless without me. In the same way, God used men to record the Word of God, but it was His Word, not theirs, and they never added to it or took away from it. They understood the seriousness of trying to distort God’s Word. The manuscripts really are God’s Word, and they’ve been preserved for us for these last few thousand years. And it is just a truthful and reliable today than when the first words were penned. The Word of God abides forever, and for that, we should thank God, because they contain the words of life. Jesus said, “You search the Scriptures because you think that in them you have eternal life; and it is they that bear witness about me” (John 5:39), so it really is the Word of God and not the word of men.
Here is some related reading for you: How do we Know the Bible is True? Is it Really the Word of God? 
Resource – Scripture quotations are from The Holy Bible, English Standard Version® (ESV®), Crossway Bibles. (2007). ESV: Study Bible: English standard version. Wheaton, Ill: Crossway Bibles. Used by permission. All rights reserved.