“If so, then what is the purpose of witnessing? To what end do we spread the gospel?”
Ask Spurgeon, one of the greatest evangelists that ever lived, who believed the Gospel message as delivered to us by the Apostles, as believed by men like Augustine, and as held by all the reformers who fought and died to deliver us from the false doctrines of Rome. Every single one of them believed that salvation was the work of God from the beginning to the ending, according to His own plan of election before the foundation of the world.
For the Christian, what greater happiness is there but to serve God by spreading His truth as we are commanded? What greater joy for the Christian is there than to work together with God according to His plan of election? It is God who works through the preaching of His Word, and who are we to resist it? The faith which we receive from God is an effectual and living faith, which drives us towards the production of good fruit, though we are ourselves produce it not, but God who works in us.
You didn’t answer my question.