Paul was in Athens and his preaching came to the attention of lazy intellectuals who:
“took him, and brought him unto Areopagus, saying, May we know what this new doctrine, whereof thou speakest, is?” (Acts 17:19).
Paul didn't need an invitation to preach. He only needed an audience that would hold still long enough. But here was an invitation, and he wouldn't pass it up. He preached with both power and clarity to these idolaters the true nature of God:
“[He] made the world and all things therein, seeing that he is Lord of heaven and earth, dwelleth not in temples made with hands; Neither is worshipped with men's hands, as though he needed any thing, seeing he giveth to all life, and breath, and all things; And hath made of one blood all nations of men for to dwell on all the face of the earth, and hath determined the times before appointed, and the bounds of their habitation . . .” (Acts 17:24-26).
The Areopagus at which Paul was speaking was on Mars' Hill. Paul, in this place, surrounded by people who "spent their time in nothing else, but either to tell, or to hear some new thing" (Ats17:21), does not hesitate an instant.