I know that DA Carson wrote a book on this issue, but I haven’t read it. Here’s another segment from the letter I wrote to a friend a while back. If you wish to see the first two segments, scroll down the page.
How is my belief in God’s sovereignty an aid in witnessing? Because Jesus has other sheep that are not of this fold; he must bring them also, and they will listen to his voice (John 10:16). “Therefore, we are ambassadors for Christ, God making his appeal through us” (2 Corinthians 5:20). When we speak, God raises the dead. His word will accomplish the purpose for which he sent it (Isaiah 55:11), and when that purpose is the regeneration of dead hearts, then let all the powers of hell and human rebellion assemble themselves; they will be before the Lord as dust before a hurricane.God wants your friend saved? Then preach as well you can, but do not worry about your stammering tongue, your faulty memory, your inadequate display- God will move. “For the word of the cross is folly to those who are perishing, but to us who are being saved it is the power of God,” (1 Corinthians 1:18), and “we are the aroma of Christ to God among those who are being saved and among those who are perishing, to one a fragrance from death to death, to the other a fragrance from life to life” (2 Corinthians 2:15-16). When we preach the Word, it hardens some to death and wakens others to life, and it is not for us to decide which is which. He has mercy on whomever he wills, and he hardens whomever he wills (Romans 9:18). He has mercy. He has mercy.And over all of history stands the promise, the certainty that someday there will be “a great multitude that no one could number, from every nation, from all tribes and peoples and languages, standing before the throne and before the Lamb, clothed in white robes, with palm branches in their hands, and crying out with a loud voice, ‘Salvation belongs to our God who sits on the throne, and to the Lamb’” (Revelation 7:9-10). Think of it! Someday you will stand shoulder to shoulder with men and women from places where there is no gospel, from tribes right now in bondage to the spirit of the age- you will stand redeemed before the Desire of nations and you will worship him! The song of praise to the Lamb will resound through eternity is English and Korean and Farsi and Zulu and languages never before heard to Western ears!This is not a vain hope, and it’s not a goal we would like to accomplish- he will do it! And he will use you. He will use you. You. You can say with Paul “Of this gospel I was made a minister according to the gift of God’s grace, which was given me by the working of his power. To me… this grace was given, to preach to the Gentiles the unsearchable riches of Christ, and to bring to light for everyone what is the plan of the mystery hidden for ages in God who created all things, so that through the church the manifold wisdom of God might now be made known to the rulers and authority in the heavenly places. This was according to the eternal purpose that he has realized in Christ Jesus our Lord, through whom we have boldness and access with confidence through our faith in him” (Ephesians 3:7-11).