John 16:8 "And when He has come, He will convict the world of sin, and of righteousness, and of judgment:"
Our Lord referred to non believers and nominal and worldly Christians as the world whom the world loves.
John 15:19 "If you were of the world, the world would love its own. Yet because you are not of the world, but I chose you out of the world, therefore the world hates you."
For the Spirit of truth to convict the world, our testimonies must be the truth and the gospel preached must comprise of these three elements: sins, righteousness and judgment.
John 16:9 "of sin, because they do not believe in Me;"
During our witnessing when we mention or remind them of their sins and abominations which separated them from God the Father, the Spirit of truth or the Helper will be able to convict them of their sins. This may lead them to their salvation by believing in our Lord Jesus.
1Pet 4:3-4 For we have spent enough of our past lifetime in doing the will of the Gentiles—when we walked in lewdness, lusts, drunkenness, revelries, drinking parties, and abominable idolatries. In regard to these, they think it strange that you do not run with them in the same flood of dissipation, speaking evil of you.
John 16:10 "of righteousness, because I go to My Father and you see Me no more;"
We must preach the message of the cross that by the death of our Lord Jesus on the cross, He has redeemed us from our sins and from death and by His resurrection we are empowered with His Holy Spirit to live righteously and holy to His glory.
Col 1:19-23 For it pleased the Father that in Him all the fullness should dwell, and by Him to reconcile all things to Himself, by Him, whether things on earth or things in heaven, having made peace through the blood of His cross. And you, who once were alienated and enemies in your mind by wicked works, yet now He has reconciled in the body of His flesh through death, to present you holy, and blameless, and above reproach in His sight.
John 16:11 "of judgment, because the ruler of this world is judged."
At the death of our Lord Jesus on the cross, the devil was judged. Death, damnation, the fire of hell and the devil no longer has power over Christians, who are the children of God. We are also set free from the fear of death - knowing that there is no longer any death but the final joyful eternal life with God the Father in heaven.
Heb 2:14 Inasmuch then as the children have partaken of flesh and blood, He Himself likewise shared in the same, that through death He might destroy him who had the power of death, that is, the devil, and release those who through fear of death were all their lifetime subject to bondage.
Brethren, this is the gospel of our Lord Jesus Christ, which many covetous pastors, televangelists and false prophets have diluted and adulterated it. But I fear, lest somehow, as the serpent deceived Eve by his craftiness, so your minds may be corrupted from the simplicity that is in Christ. For if he who comes preaches another Jesus whom we have not preached, or if you receive a different spirit which you have not received, or a different gospel which you have not accepted—you may well put up with it!. (2Cor 11:3-4)