"Then the deputy, when he saw what was done, believed, being astonished at the doctrine of the Lord."–Acts 13:12
The Gospel is the power of God unto salvation. Like a lion, you don’t have to defend it, or debate it. Just turn it loose, and it will defend itself.
As Paul and Barnabas began their first missionary journey and were immediately confronted with opposition, yet the Lord proved the power of His Word in converting a deputy in Cyprus, in spite of strong opposition from one of the local sorcerers. God sovereignly condemned the sorcerer to blindness, but graciously opened the heart of the deputy to the truth.
Men naturally oppose the Gospel because it gives God all the glory. It is the doctrine of the Lord. It describes Him as Lord in creation, providence, salvation, and judgment. It is not a message of "He is Lord, if you’ll let Him," but, "He is LORD, and you will bow, either now, or in hell. Why wasn’t Elymas, the sorcerer saved? Because of the hardness of his heart. God judged him in leaving him in blindness. He is just in dealing with sinners in this way, should He so please. Why was Sergius Paulus converted? The text says clearly, that he "believed, being astonished [literally, flattened out] by the doctrine of the Lord (the Gospel). In the hands of the sovereign Spirit of God, the Gospel knocks the sinner down and lays him, taking from him all hope in self. 1). All self-glorying gives place to glorifying God alone as Lord and Savior, Isaiah 6:5.
2). All self-worth is laid in the dust, acknowledging that Christ the Lamb alone is worthy of praise in redeeming and sanctifying the sinner, Romans 9:5-12.
3). All self-effort gives place to resting in the satisfaction of the Law which Christ alone procured for His own, Galatians 2:21. Has the Gospel laid you low, or do you continue to defend your own self-worth, self-will, and profession? God will not share His glory with another! Isa 48:11 "For mine own sake, even for mine own sake, will I do it: for how should my name be polluted? and I will not give my glory unto another."