Should we conclude that preaching of the gospel is a waste of time and write off evangelism as a hopeless enterprise, foredoomed to fail? No, because the Spirit abides with the church to testify of Christ. To the apostles, he testified by revealing and inspiring, as we saw. To the rest of us, down the ages, he testifies by illuminating: opening blinded eyes, restoring spiritual vision, enabling sinners to see that the gospel is indeed God's truth, and Scripture is indeed God's Word, and Christ is indeed God's Son. "When he [the Spirit] comes," our Lord promised, "he will convince the world concerning sin and righteousness and judgment" (Jn 16:8 RSV).
It is not for us to imagine that we can prove the truth of Christianity by our own arguments; nobody can prove the truth of Christianity except the Holy Spirit, by his own almighty work of renewing the blinded heart. It is the sovereign prerogative of Christ's Spirit to convince men's consciences of the truth of Christ's gospel; and Christ's human witnesses must learn to ground their hope of success not on clever presentation of the truth by man, but on powerful demonstration of the truth by the Spirit.
— J.I. Packer, Knowing God
Praise God