Human beings speak with their mouths as their breath moves across their vocal cords, causing the cords to vibrate and produce sounds that are formed into letters and words by our lips, tongues, and teeth. There is a breathing out that has to take place for speech, and understanding this reality helps us to understand Paul's point in today's passage. Scripture, he tells us, results from God's breathing out in speech. This is a rather clear way of saying that Scripture is the very speech of God. It is His Word.
The Greek word translated as "breathed out" in 2 Timothy 3:16 is theopneustos, and Scripture is the only thing described as such by the Apostles. Thus, Scripture has a unique character as the voice and words of the Lord. It uniquely serves as God's special revelation, as His inspired and revealed will for His people. Nothing else today is theopneustos, so we can point to nothing but Scripture as the Word of God.
When we speak of Scripture as theopneustos, we are pointing to its divine inspiration. The Word of God written is identical to God's speech. It is exactly what He intended us to have as the revelation of His will and how to please Him. At the same time, this does not take away from the Bible's human character. God breathed out His Word, but He did so through the instrumentality of His prophets and Apostles. So, for example, the book of Romans is Paul's word, bearing the Apostle's unique style and character. Nevertheless, it is also God's Word, given by Him. That our Lord used a man to give us the book of Romans does not in any way make it less than the very speech of God. And this applies to all books of Scripture.
Following 2 Timothy 3:16 and other passages, the Protestant Reformers affirmed verbal plenary inspiration. Verbal inspiration means that inspiration pertains to the very words themselves, not just the meaning that the words convey. If Jesus could appeal to the tense of a verb in order to settle a theological question ("I am the God of . . ."; Matt. 22:23–33), inspiration must apply to specific words and even their specific forms. Plenary inspiration means that all the words of Scripture are given by God, not just some of them. We cannot say that the Lord spoke only the words of Scripture that pertain to doctrine but not those that record history. No, God spoke it all, using the distinct style of each human author to give us His Word for all of life. Paul says all Scripture—everything received as canon—is God's Word, not just select portions of it (2 Tim. 3:16).
The process of biblical inspiration is mysterious, for we do not know exactly how God moved the human authors of Scripture to give us His Word. Nevertheless, we know that Scripture is the Word of God, and so it can be trusted to give us nothing but the truth of God. When we want to know God's will for us, we must turn to Scripture, for it is there alone that we will find the Lord's guidance.