In the major cities there were a number of Gentiles who were strongly attracted to Judaism but who were unwilling to convert to Judaism. Known variously in ACTS and other ancient sources as God-fearers, God-worshipers and God-lovers, they were Gentiles involved in but still on the fringe of Judaism. They often attended synagogue services and thus knew quite a bit about Judaism, its scriptures, rituals, festivals, yearnings and vision. Some became benefactors. No doubt they had Jewish friends. But the men did not get circumcised and households may or may not have observed Jewish food and purity laws.
That Gentile God-lovers were Paul’s primary audience not only is affirmed by ACTS and implied in his letters, but also makes good sense. The Gentiles to whom he had the most immediate access were the God-lovers whom he would find in synagogues. So when Paul arrived in a new city, he went first to the synagogue – not because his mission was to convert Jews, but because Gentile God-lovers would be there.
Paul sought to enlist these God-lovers into communities of Christ-followers either by creating a new community in that city or by integrating them into an existing community. Christian groups existed in some cities before Paul got there, including Ephesus and Rome. In others, they were Paul’s creation.
Other then synagogues, the other context in which Paul encountered  Gentiles was in his work. Paul supported himself by tent-making, an umbrella term that included making awnings, in great demand in the Mediterranean world, and perhaps more generally in making leather goods. Paul’s skill gave him great mobility and self-sufficiency. The basic tools could be carried in a waist bag. He could travel light and find a job in any significant city. No doubt Paul met some of his Gentile converts while working next to them in a shop.
This understanding of Paul’s audience should affect our image of how Paul preached Jesus. Because of modern images of preaching, we tend to think of Paul standing in front of a crowd, large or small, and proclaiming the Gospel. ACTS sometimes portrays Paul this way; he preaches in synagogues and even in a theater filled with 20,000 people. But it is unlikely that Paul preached in synagogues or to crowds of strangers who were completely unfamiliar with Judaism. What would his message, which make so much use of Jewish language and tradition, have meant to Gentiles who knew nothing abo0ut Judaism?
We need to imagine Paul’s approach as much more conversational. This, I believe, is essential if we are to come to a true understanding of Paul and of his writings, ministry and preaching.