John 17:17
Sanctify them by Your truth. Your word is truth.
Jesus, praying to the Father, gives a clear and straightforward definition of truth: God's Word. The Holy Bible (Scripture—the word of truth) was given by inspiration of God (2 Timothy 3:16). The Greek expression translated "inspiration of God" literally means "God-breathed"! He actively and fully inspired the Bible to reveal His truth to us.
His promises, His commands, His word—they are all truth, plain and simple. After all, "The LORD of hosts has purposed, and who will annul it? His hand is stretched out, and who will turn it back?" (Isaiah 14:27). If God says something, there is no force that can stop Him from doing it—we can rest assured that it will be done.