Visitor: if election is true, why preach the gospel?
Response: why preach the gospel? because "election" saves nobody by itself. Salvation is by Christ. Election is merely a blueprint of what God intends to do in history through Christ. The Father elects, the Son redeems and the Spirit quickens and unites the sinner to Christ through the gospel.
The gospel is like a seed. We cast the seed indiscriminately, as God commands, and it goes into the heart of man... but unless the Holy Spirit germinate the seed, so to speak, it falls on fallow ground. 'No one says 'Jesus is Lord' apart from the Holy Spirit." (1 Cor 12:3)
Jesus declared, "all that the Father give to me will come to me" John 6:37
Notice, Jesus says the Father giving them to the Son precedes their coming to faith in him... in addition Jesus says all, not some, but all that the Father gives to Jesus come to faith in him.
The main difference in understanding the bible is between monergism and synergism. .. does Jesus provide everything we need for salvation, including a new heart to believe (Deut 30:6; Ezek 36:26; John 6:63), or does Jesus only provide some of what we need? Does Jesus rescue us or help us rescue ourselves?
The issue is all about whether we are saved by Christ alone or not .. and the answer is in Scripture, the Christians' sole authority.
God has made us the means and instruments by which God disseminate the live-giving gospel. We are not called to discover who the elect are or to be concerned with the ultimate results, but to faithfully go about sowing the seed of the gospel. He will take care of produce the crop. The Apostle Paul said, "I planted, Apollos watered, but God gave the growth. So neither he who plants nor he who waters is anything, but only God who gives the growth." (1 Cor 3:6-7)
If, as some people think, God provides equal opportunity to believe for all people on earth, then why send missionaries? The Bible teaches that it is through the preaching of the gospel that God gathers up his elect.
"It pleased God through the foolishness of preaching to save those who would believe." (1 Corinthians 1:21)
"How then will they call on him in whom they have not believed? And how are they to believe in him of whom they have never heard? And how are they to hear without someone preaching? So faith comes from hearing, and hearing through the word of Christ." (Romans 10:14, 17)