All scripture is given by inspiration of God, and is profitable for doctrine, for reproof, for correction, for instruction in righteousness, 2nd Timothy 3:16.
Before we begin looking at our key word "reproof", it is interesting to look at how modern versions botch 2nd Timothy 3:16.
NIV: All Scripture is God-breathed and is useful for teaching, rebuking, correcting and training in righteousness.
"God breathed" obscures how God transmits scripture and understanding. God is on the inside of the person to whom he would transmit scripture or give understanding. The proper word here is "inspiration". All scripture is given by "inspiration of God. That means God's intake of breath. Breathing is composed of two acts, men inspire or breath in air, and then they expire, they breath out air. The second grievous point is that the NIV substitutes "rebuking" for "reproof". They are not the same thing.
ESV: All Scripture is breathed out by God and profitable for teaching, for reproof, for correction, and for training in righteousness.
Here the ESV gets reproof right, but they tell us the opposite of what the word of God says about the transmission of scripture. The ESV has God blowing scripture into men. Our bible, the King James Bible has God inside of the person and drawing scripture and understanding into him by the act of breathing in.
Reproof is another of the properly chosen and perfectly fitted words to give us the "exact translation" that the translators proclaimed upon completion of the King James Bible. In English "reproof" is the noun and "reprove" is the verb. They are used often and well in our bible. Like many English words their meanings have evolved over the years and dictionaries are wont to confound the the definitions as being the same as definitions as rebuke or rebuking.
This is one of those times when it is important for the student who would understand his bible to cross reference many places wherein either reproof or reprove have been used to understand what the King James translators were thinking when they used either word. The simplest and most effective way to understand what a word means is to see it or hear it in multiple uses and to gain understanding by the context in which it was used. That is how we originally learned the languages of our youth. When I am watching a British movie or television show, I only need to hear the rear storage space in a vehicle referred to as the "boot" a couple of times before I realize that they are referring to what I would have called the "trunk".
Of the few meanings of reproof in the Oxford English Dictionary one meaning stands out that will fit each application on our King James Bible.
Reproof: Cause for censure; fault, blame. Another defintion that fits is: Disproof, refutation.
We can be certain that the translators did not mean for reprove and rebuke to be synonymous because they use both words in one verse as two distinctly different things. Preach the word; be instant in season, out of season; reprove, rebuke, exhort with all longsuffering and doctrine, 2nd Timothy 4:2. It is clear that they had two distinctly different meanings in mind when they gave us our bible.
To reprove someone is to show them their fault. By reproving someone, a preacher can show them what about their behavior would open them up to censure or to be found blameworthy. The rod and reproof give wisdom, Proverbs 29:15. To just beat or otherwise punish a child does nothing but engender wounds, psychological damage and bitterness. To reprove a child may carefully show them what about their behavior is displeasing or harmful, but it will go in one ear and out the other. It is the combination of careful instruction backed up by corrective discipline that makes a child wise.
Whereas reproof shows us the cause for censure, to rebuke is to deliver the censure. When Peter transgressed at Antioch, the Apostle Paul explained to him why he was upset with him. It wasn't just a one line rebuke, he took time to make Peter see the point in which he was wrong and why he was wrong.
Gal 2:11 But when Peter was come to Antioch, I withstood him to the face, because he was to be blamed.
Gal 2:12 For before that certain came from James, he did eat with the Gentiles: but when they were come, he withdrew and separated himself, fearing them which were of the circumcision.
Gal 2:13 And the other Jews dissembled likewise with him; insomuch that Barnabas also was carried away with their dissimulation.
Gal 2:14 But when I saw that they walked not uprightly according to the truth of the gospel, I said unto Peter before them all, If thou, being a Jew, livest after the manner of Gentiles, and not as do the Jews, why compellest thou the Gentiles to live as do the Jews?
Galatians 2:15 We who are Jews by nature, and not sinners of the Gentiles,
Galatians 2:16 Knowing that a man is not justified by the works of the law, but by the faith of Jesus Christ, even we have believed in Jesus Christ, that we might be justified by the faith of Christ, and not by the works of the law: for by the works of the law shall no flesh be justified.
Galatians 2:17 But if, while we seek to be justified by Christ, we ourselves also are found sinners, is therefore Christ the minister of sin? God forbid.
Galatians 2:18 For if I build again the things which I destroyed, I make myself a transgressor.
Galatians 2:19 For I through the law am dead to the law, that I might live unto God.
Galatians 2:20 I am crucified with Christ: nevertheless I live; yet not I, but Christ liveth in me: and the life which I now live in the flesh I live by the faith of the Son of God, who loved me, and gave himself for me.
Galatians 2:21 I do not frustrate the grace of God: for if righteousness come by the law, then Christ is dead in vain.
Rebukes are sharp and usually come with one or two lines. But he turned, and rebuked them, and said, Ye know not what manner of spirit ye are of, Luke 9:55. These distinctions become important if you want to raise a family, pastor a church or even to understand doctrine as we shall soon see.