In verses 9-11 this is elaborated upon a little by the Lord: ‘Of sin, because they believe not on me.’ Now some people have taken this too far.
Now the great thing we must preach about is sin. I remember hearing a well-known evangelist, no longer alive, saying (this is some years ago), ‘It is a great mistake to put too much emphasis on sin.’ His reasoning, his thoroughly human reasoning, was quite sound, because people find it objectionable and you will not raise crowds, and you will not get a hearing, but his solution was therefore, ‘Do not preach too much about sin.’ But what Christ tells his disciples, and us, is, ‘Preach about sin; witness to me, because as you do so the Holy Spirit will convict within.’ That is the difference. Yes, it is unwanted, but if you want the work of the Spirit, you must preach the things that the Spirit wants to do. He wants to convict of sin. And people will be saved.