To take God at His Word is to accept and trust what God has said because God is the One who has said it.If I take you at your word I am demonstrating that I respect and trust you. The same holds true when we take God at His Word: we demonstrate that we respect and trust Him.
What the Bible says about itself:
Let’s begin with the fact that the Bible is inspired: it is God-breathed, exhaled from God. All Scripture is God-breathed and is useful for teaching, rebuking, correcting and training in righteousness, so that the servant of God may be thoroughly equipped for every good work. (2 Tim. 3:16–17)
And yes, the Word of God comes to us through God’s self-revelation in cooperation with human agents who literally wrote it down. But those authors weren’t writing down whatever came to mind. They were recording the things God inspired them to write.
2 Peter 1:20-21 says:
“Above all, you must understand that no prophecy of Scripture came about by the prophet’s own interpretation of things. For prophecy never had its origin in the human will, but prophets, though human, spoke from God as they were carried along by the Holy Spirit.”
But how can we know it’s true? Because God is Truth.
Again, looking at what the Bible says about itself on this point of truthfulness we read: Every word is described as flawless (Ps. 12:6; Prov. 30:5), eternal (Ps. 119:89; Isa. 40:8; Matt. 24:35), unbreakable (John 10:35), boundless in perfection (Ps. 119:96), and completely reliable (2 Pet. 1:19). Jesus affirmed it concisely: “[God’s] Word is truth” (John 17:17).
Scripture’s truthfulness is so comprehensively assumed, in fact, that entire arguments can hinge on appeals to a single word (Matt. 22:45), the number of a noun (Gal. 3:16), even the tense of a verb (Matt. 22:32). See also Ps. 12:6; 19:7–9; 119:160; Prov. 30:5–6; John 10:35; 17:17
And if God is the Author, then the Bible is authoritative. It is not a matter of whether or not you believe it, the question is whether or not you obey the One who is the Author of it. The Bible is authoritative because God is the Author, and God has all authority of all things.
James 1:22 puts it most succinctly, “Do what it says.”
And the Bible is also sufficient. You don’t need to add anything to it. You don’t need additional testaments or revelations or prophets who come later in history. The Bible contains all the words of God you need to know, relate to, obey, abide in, enjoy and glorify God fully.
Peter says God has given us “everything we need for a godly life” through the knowledge available in the Bible (2 Pet. 1:3). And Paul says the Bible is so complete that through it we can be “thoroughly equipped for every good work” (2 Tim. 3:16). Thoroughly, not partially or part way. The Bible is thoroughly sufficient.
The Bible is also effective. It is an instrument of God’s power. John says it is powerful enough to change lives (John 17:17). Paul echoes that message in Rom. 1:16 and 1 Thess 1:4–5. Jeremiah says God’s Word is powerful enough to melt hearts (Jer. 23:29).Hebrews says it this way:
“The word of God is alive and active. Sharper than any double-edged sword, it penetrates even to dividing soul and spirit, joints and marrow; it judges the thoughts and attitudes of the heart.” (Heb. 4:12)
And, I think it’s also important to recognize that the entirety of the Bible is ultimately not about us and our salvation but Jesus, the Savior. The story of the risen Christ in what we call the walk to Emmaus in Luke 24 says,
“How foolish you are, and how slow to believe all that the prophets have spoken! Did not the Messiah have to suffer these things and then enter His glory?”
And beginning with Moses and all the Prophets, He explained to them what was said in all the Scriptures concerning Himself. (Luke 24:25–27)
And later, He says again to His 11 disciples,
“This is what I told you while I was still with you: Everything must be fulfilled that is written about me in the Law of Moses, the Prophets and the Psalms.”
Then He opened their minds so they could understand the Scriptures. (Luke 24:44–45)
Every word of God PROVES true because God is truth –and by His great love, He has chosen to reveal Himself and everything we need to know for salvation in the Bible.