Witnessing for Christ is the responsibility of every believer. Acts 1:8; 1 Pet. 3:15; Mk. 5:18,19.
The effectiveness and clarity of the believer's witnessing depends, in large measure, on his understanding of the Last Judgment. Sins will not be the issue! The only reason that a person will stand at the Last Judgment is that he rejected Christ during his lifetime. John 3:18; 3:36. All sins have been judged at the Cross, and there is no double jeopardy.
The basis for the indictment of unbelievers is human good, not sins. The witnessing Christian must make the issue clear.
Witnessing is impossible apart from the filling of the Holy Spirit. John 16:8-11. And the Holy Spirit must minister to the unbeliever to apply the doctrine of salvation.
The context for witnessing is that part of the Word of God called the Gospel. 1 Cor. 1:18; Eph. 6:17; Heb. 4:12.
The dynamics of witnessing depends on the believer's mental attitude. One cannot be an effective witness if he is ashamed of the Gospel, if he does not have the capacity to be occupied with Christ, or if he is not oriented to Grace.
In Rom. 1:14-16, the apostle Paul says "I am debtor", "I am ready", and "I am not ashamed". A fisherman has a desire to fish. One is not a "fisher of men" without a desire to win souls.
There are two sources for a Christian's witness: (1) the testimony of his life, 2 Cor. 3:3, and (2) the testimony of his lips, 2 Cor. 5:14-21.
There is a reward for witnessing. 1 Cor. 3:11-16; 2 Cor. 5:10. Rewards in heaven are an extension of edification; the only things that are rewarded in heaven is what is done on the basis of Grace. Thus, every reward in heaven is an eternal memorial to the grace of God. Grace means that rewards do not reflect any personal glory or merit. It is the Lord who enables us to labor for Him and who provides the divine production in the life (gold, silver, and precious stones).