Because there are over 14,000 manuscript copies of the New Testament we can absolutely be confident of its accuracy. With this large number of manuscripts, comparing manuscripts easily reveals any place where a scribe has made an error or where there is a variation. There are approximately 150,000 variations in the manuscripts we have today. However, these variations represent only 10,000 places in the New Testament (if the same word was misspelled in 3,000 manuscripts, that is counted as 3,000 variations.) Of these 10,000 places, all but 400 are questions of spelling in accord with accepted usage, grammatical construction, or order of words. Of the remaining variations, only 50 are of significance (such as two manuscripts leaving out Acts 2:37). But of these 50, not one alters even one article of faith which cannot be abundantly sustained by other undoubted passages.

There are some manuscripts that date as early as 130 AD, very close to the completion of the New Testament. These manuscripts are nearly identical to those dating 900 years later, thus verifying the accuracy of the scribes.

God also promised to preserve His words.
The words of the LORD are pure words: as silver tried in a furnace of earth, purified seven times. Thou shalt keep them, O LORD, thou shalt preserve them from this generation for ever. (Psalms 12:6-7)

You shall not add or take away, says God.
Now therefore hearken, O Israel, unto the statutes and unto the judgments, which I teach you, for to do them, that ye may live, and go in and possess the land which the LORD God of your fathers giveth you. Ye shall not add unto the word which I command you, neither shall ye diminish ought from it, that ye may keep the commandments of the LORD your God which I command you.(Deuteronomy 4:1-2)

God cares about every one of His words.
Every word of God is pure: he is a shield unto them that put their trust in him. Add thou not unto his words, lest he reprove thee, and thou be found a liar. (Proverbs 30:5-6)

God’s words will never pass away.
Heaven and earth shall pass away: but my words shall not pass away. (Jesus Christ, Son of God) (Mark 13:31)

God will curse those who change His Word.
For I testify unto every man that heareth the words of the prophecy of this book, If any man shall add unto these things, God shall add unto him the plagues that are written in this book: And if any man shall take away from the words of the book of this prophecy, God shall take away his part out of the book of life, and out of the holy city, and from the things which are written in this book. (Revelation 22:18-19)