I just heard a speech on the usefulness of the word of God today. Just a short excerpt. And I totally so agree with Annsan_In_Him
But then we're looking at this second statement, "All Scripture is useful...useful, profitable," to produces these five things. According to verse 15 it can make you wise unto salvation and according to verse 16 it is profitable, or useful for doctrine, reproof, correction and training and is the only thing needed and the only thing able to make the man of God perfect, equipped for every good work.
Now, beloved, that's another statement like Psalm 19 on the sufficiency of Scripture. What this says to us is the Scripture is comprehensively sufficient to produce men of God for every good work. It knows no limitation. It has no weakness. Nothing is left out. Nothing can be added to it. Such an attempt, by the way, according to Revelation 22 winds up with a warning, if you add anything to this, so shall be added to you the plagues that are written in it. The Bible is not to be tampered with, it is not to be distorted, it is not to be corrupted, it is not to be manhandled for your own purposes and it is not to be added to.
Now let me say it as simply as I can. When it comes to spiritual life, when it comes to a person's relationship to God, the Bible is all that is necessary for proper instruction to make the man of God complete and capable of every good work. It is not the Bible plus anything. And that is why we are so committed to the systematic ongoing teaching of God's Word, because of what it does.
Now we've entitled these five things "the work of the Word." What does the Word do? First of all, remember in verse 15, it is able to make you wise unto salvation. The Word has the power to save. The Word of Christ is that which is necessary for salvation, Romans 10 says. It is the Word of God, 1 Peter 1, by which you are begotten again. It is the Word which brings the gospel. It is the Word which in the power of the Holy Spirit brings new life. It is the Word which saves. And so last time we said above all things we must be committed to the proclamation of God's Word to the lost, for the Word is able to make them wise unto salvation.
Secondly, and coming in to verse 16, he says it is useful for doctrine or for teaching. And I pointed out to you that here he has in mind not the process of teaching but the content. It is profitable to give you the necessary body of divine truth to live a godly life. That's what he's saying. The Bible provides for you what Paul calls to Timothy the deposit. It gives you the truth, the deposit of truth to be guarded, 1 Timothy 6:20 and 21, 2 Timothy 1:13. It is God's revelation of truth. And it provides for you the substance to be believed...doctrine, the body of content upon which...mark this carefully...every thought and every action is to be built. Did you get that? The Bible provides for us the body of truth upon which every thought and every action is to be built. So it is profitable for content. It gives us the truth. John 17:17, "Thy Word is truth." If you're looking for a foundation to build your life on, it is this book. It provides the principles that are to operate in the life of every individual at every point of need and demand, thought and action. It's comprehensive. Every single thing you will ever deal with in your spiritual existence is covered one way or another in the Scripture, probably many more than just one time. It is replete with instruction for life...life in the way that God has designed it.
So, it is profitable and useful to provide for you the body of divine doctrine. And as I said last time, as you study the Word of God and begin to accumulate its principles, you begin to build that strong foundation which then becomes the foundation on which every thought and every action is built. Biblical ignorance is the grave tragedy of all tragedies in the church because what you don't know you can't build your life on. So it ought to be then the pursuit of every believer to know the Word of God, to as much as is possible master the Word of God. (John MacArthur on 2 Tim. 3:16 1988)