Acts 17, where Paul is in Athens and directly speaks to those who do not hold scripture as authoritative has always held a special part in my evangelistic walk. I love the scriptures. I love them! I don't want anyone to consider the opposite but I love how Paul plants the seed for the scriptures by finding common ground with people who do not love the scriptures.
Paul always taught at the Temple first and would use scripture for Jews but for those that are "outsiders" he takes a different approach but in the finding of common ground he does not dilute the power of the Gospel. It is simply put into words that the people could understand. Understanding the Gospel is key in accepting it... if the audience or person we are addressing does not understand it than the chances of them following are minimal. Common Ground Evangelism is powerful.
In Acts 17: 16-34 (you should read), we notice that Paul takes note of the idolatry that this society is falling under. But instead of addressing it as a sin, he uses it because of an alter marked to an "unknown God". He capitalizes on the Unknown God and points to the right and Worthy God, the True God. It reminds me of how Jesus spoke to the Samaritan woman at the well in John 4. He did not address her sin when she first approached Him and in fact He didn't address her sin until after she admitted to being husbandless. When our evangelism starts off with a pointing finger and condemning people who do not know scripture (and some who know some scripture) it instantly turns them away. Jesus and Paul find common ground. Jesus found common ground in the need for water, which turned into living water. Paul finds common ground with the need to know the true God.
Do we (the church as a whole, not individuals) find common ground before pointing fingers?
Did we find common ground with the same sex parties who fought for equal rights or did we declare them condemned and sinful. We took no time to find their need, we just addressed the sin.
Did we find common ground with Muslims before we deemed them unworthy of helping and aiding as they run from terrorists? Did we take time to address their need or did we just deem them not worth witnessing too?
Paul's approach here should be used and yet the church just simply sits back and points fingers at sin now. We don't even get to the part about our God forming and making all that is creation, we don't give the gospel to people, we do not tell people that our God wants them as His children... we simply tell them that He hates their sin.
In verse 30-31, Paul calls people to repent after telling them the story about a God who loves them, who wants them. And He warns about the coming judgement. Some laughed at the thought of resurrection, some needed more information, some accepted and followed. But if Paul's goal was simply to clear idolatry instead of give the Gospel... would he have had anyone accept? I don't think so.
Find the common ground and battle for the soul not against the sin. The Holy Spirit will correct the sin after acceptance of the Gospel but they have to understand why they must give up the sin to see it as sin. The Gospel must be presented.