2 Timothy 3:16: All scripture is given by inspiration of God, and is profitable for doctrine, for reproof, for correction, for instruction in righteousness:
John 16:7: Nevertheless I tell you the truth; It is expedient for you that I go away: for if I go not away, the Comforter will not come unto you; but if I depart, I will send him unto you. 8 And when he is come, he will reprove the world of sin, and of righteousness, and of judgment: 9 Of sin, because they believe not on me; 10 Of righteousness, because I go to my Father, and ye see me no more; 11 Of judgment, because the prince of this world is judged.
2 Timothy 4:2: Preach the word; be instant in season, out of season; reprove, rebuke, exhort with all longsuffering and doctrine.
We get reproof from the Bible, the Holy Spirit, others who obey the Bible and we are commanded to give it to others. It is obviously important and beneficial. We should desire it, seek it, receive it and give it. So what is it? to confute, admonish, convict, convince, tell a fault and or rebuke. The Holy Spirit reproves and does it for important reasons. Unbelievers need it because they believe not on Jesus. It is necessary to bring them to faith. Without reproof, faith and righteousness, they will never be with Jesus in Heaven and they will go into everlasting fire prepared for the Devil, the prince of this world, and his angels.
Matthew 25:41: Then shall he say also unto them on the left hand, Depart from me, ye cursed, into everlasting fire, prepared for the devil and his angels:
Along with reproof the Bible and the Holy Spirit give us doctrine, correction and instruction in righteousness. They teach us what to do and what not to do.
Proverbs 1:23: Turn you at my reproof: behold, I will pour out my spirit unto you, I will make known my words unto you.
God*s reproof will cause men to turn away from sin and to God, to repent, and they are given the Holy Spirit and understanding of God*s Word. Rejecting His reproof is dangerous.
Proverbs 1:25: But ye have set at nought all my counsel, and would none of my reproof: 30 They would none of my counsel: they despised all my reproof.
Proverbs 5:11: And thou mourn at the last, when thy flesh and thy body are consumed, 12 And say, How have I hated instruction, and my heart despised reproof;
Proverbs 10:17: He is in the way of life that keepeth instruction: but he that refuseth reproof erreth.
Proverbs 12:1: Whoso loveth instruction loveth knowledge: but he that hateth reproof is brutish.
Proverbs 13:18: Poverty and shame shall be to him that refuseth instruction: but he that regardeth reproof shall be honoured.
Proverbs 15:5: A fool despiseth his father*s instruction: but he that regardeth reproof is prudent. 10 Correction is grievous unto him that forsaketh the way: and he that hateth reproof shall die. 31 The ear that heareth the reproof of life abideth among the wise. 32 He that refuseth instruction despiseth his own soul: but he that heareth reproof getteth understanding. 17:10 A reproof entereth more into a wise man than an hundred stripes into a fool. 29:15 The rod and reproof give wisdom: but a child left to himself bringeth his mother to shame.
Habakkuk 2:1: I will stand upon my watch, and set me upon the tower, and will watch to see what he will say unto me, and what I shall answer when I am reproved.