"All Scripture is given by inspiration of God, and is profitable for doctrine, for reproof, for correction, for instruction in righteousness:" (2 Tim. 3:16)
The word reproof means 'convict.' It is to prove beyond a reasonable doubt a person's sins and failures. This is the 'hard side' of the use of the Bible. In soulwinning, we dare not skip over the need to show lost sinners the reality of their spiritual condition (which is dead). We cannot neglect to tell them about the penalty of sin. Sometimes in dealing with our brothers and sisters in Christ, we need to use the Bible to show them the error of their ways. If we try to 'work' with them without 'reproving' them (when it is needed) basically we cannot be a help to them. We don't need to rely on our wisdom when it comes to 'reproving' any one. Use the Bible. Show them from the Bible their condition. The Bible is described as fire and hammer (Jer. 23:29), and sword (Heb. 4:12 and Eph. 6:17) among other metaphors. Our attitude in reproving should be one of meekness and wanting to help others, and our main tool in this task is the Word of God.
(The picture above is a page from the Geneva Bible - I can't find any pics with better quality, oh well, life in the big city. LOL!)