How that by revelation he made known unto me the mystery; (as I wrote afore in few words Whereby, when ye read, ye may understand my knowledge in the mystery of Christ) - Ephesians 3:3-4
When God gives information to man regarding His knowledge it is known as "revelation" (Ephesians 3:3). When God uses man to write down the revealed information (scripture), this is called "inspiration" (2 Timothy 3:16).
The Bible contains the knowledge of God. Regarding His word, God has magnified His word above all His name (Psalm 138:2). Among other attributes His word is pure (Psalm 12:6), His word will judge (John 12:48), and His word is able to save (1 Corinthians 15:1-2).
The function of all scripture for the believer according to 2 Timothy 3:17 is to perfect the man of God, throughly furnishing him unto all good works.
If this is the function of all scripture, it is required that all scripture be available.
The way God's words have continued hundreds of years to make it into your hands is called "preservation" (Psalm 12:6-7). We see this done via copies, not original documents (the originals are long gone).
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. - Psalm 12:6-7
God has made it plain that "Heaven and earth shall pass away, but my words shall not pass away." (Matthew 24:35, Mark 13:31, Luke 21:33) Either we believe, "the word of the Lord endureth for ever" (1 Peter 1:25), or we don't.
When it comes to the Bible working in the life of a believer, there is no room for doubting God's word. The word of God works effectually only in those who believe (1 Thessalonians 2:13).
Do you believe the words of the Bible in your hand are the pure words of the Lord?
[All Scripture quotations, unless otherwise indicated, are from the King James Bible, 1769 Cambridge Text. Used by necessity.]