God's Word is All True All the Time.
As Proverbs 30:5-6 tells us:
Every word of God is pure; He is a shield to those who put their trust in Him. Do not add to His words, Lest He rebuke you, and you be found a liar.
God has overseen His Holy Word throughout the centuries.
It comes to us, in the same manner, it was originally written.
Only God could maintain a book's accuracy throughout the generations of men.
We can believe it because it has not changed.