The other day, I wrote about why Luke goes out of his way to offer an explanation for why Paul did not evangelize in Asia, Mysia, or Bithynia during his second missionary (cf. Acts 16:6-7). We know of course that he did eventually end up working in Asia (cf. Acts 19 and the numerous references to Ephesus in the Pauline corpus), and the significance of that will be considered below. For now though, let us consider why he did not go to Asia, Mysia, and Bithynia at the time of the second missionary journey.
Let us recall my argument regarding why Luke felt that he had to explain why Paul did not evangelize in these regions at that time. I argued that this was because Luke understand that Paul was operating in accordance with an understanding of the geographic expansion of the Word from Zion, based upon early Christian exegesis of Isaiah 66:19. In this exegesis, it was understood that the Word would proceed from Cilicia, to Cyrene, to Asia, to Mysia, to Bithynia, to Greece, in that order. I further suggest that Luke understands that Paul should proceeded via that course and knows that his readers would expect that he had, and as such Luke presents Paul as doing so as best he can. He knows however that Paul did not go to Cyrene, and thus foregrounds the presence of Cyrenean Christians from the early days of the movement, and that Paul did not go to Asia, Mysia, or Bithynia, at least not when he was supposed to, and thus offers an explanation for that.
Now, here's where I begin to take a step beyond that discussion: if Luke understood that Paul should have proceeded thus, and knew that it was a common enough interpretation Isaiah 66:19 that his readers would expect that Paul should have proceeded thus, it seems highly likely that Paul in fact would have preferred to have proceeded thus. So, the first question is, Why didn't Paul go to Cyrene? The answer, I suggest, is to be found in Rom. 15:20-24: "It has always been my ambition to preach the gospel where Christ was not known, so that I would not be building on someone else’s foundation. Rather, as it is written: 'Those who were not told about him will see, and those who have not heard will understand.' This is why I have often been hindered from coming to you. But now that there is no more place for me to work in these regions, and since I have been longing for many years to visit you, I plan to do so when I go to Spain." I would propose that for the same reason that Paul had not yet traveled to Rome, neither had he traveled to Cyrene: he knew that there had already been a Christian mission in Cyrene (that a mission to Cyrene has occurred this early is a reasonable inference from the apparent presence of so many Cyreneans of Jewish descent in the early church: all it took was one of these to return home and engage in a degree of successful missionary activity for Paul to consider Cyrene another man's foundation. Moreover, we lose track of Barnabas and Mark after they set sail for Cyprus in Acts 15:38, but given the traditions that designate Mark as a Cyrenean Jew and which place him in Alexandria during the 50s and 60s, it would not be altogether insane to suggest that they proceeded to North Africa from Cyprus).
I would suggest something similar with regard to Asia, Mysia, and Bithynia: Paul did not go to these regions during his second missionary journey because he knew them to be another man's foundations. That another early Christian leader might have been involved in missionizing these regions is not mere supposition, but in fact hinted at via an independent set of data. If we look at 1 Peter 1:1, we note that he wrote specifically to the churches of Pontus, Galatia, Cappadocia, Asia, and Bithynia. With the exception of Galatia (and "Galatia" is a notoriously ambiguous regional term) this reads almost like a list of the places in Asia Minor that Paul never evangelized. Let me then advance the following suggestion: Paul does not go to these regions on his second missionary journey because he knows that Peter has already preached there.
If correct, then we can in fact pinpoint when this Petrine mission took place. It presumably post-dates the Agrippan persecution that broke out around Passover of either 41, 42, or 43 (I lean to 41, for a variety of reasons), as we have enough data on Peter's movements prior to that point that we can say with some confidence that he probably wasn't in Asia Minor. But it had to have occurred prior to Paul's arrival in Corinth, probably eighteen months prior to Gallio's arrival in July of 51. Before that, traveled through Macedonia and Greece, missions that he perhaps undertook in 49. As such, the terminus ante quem for Paul's activity in Asia Minor is probable 48ish. Since Peter was at the Jerusalem conference (Acts 15) which occurred perhaps earlier that year, 47 seems to be the absolute latest at which Peter could have evangelized in Asia Minor. As such, it appears that Peter was likely active in Asia Minor during the early to mid 40s. This incidentally probably helps to account for why Luke does not mention Peter's activity in those regions: it occurred later than the period of Peter's ministry that best fits in with the narrative that Luke wants to tell. He wants to present Peter and Paul operating in sequence, not more or less in parallel. But I digress.
It was noted above that Paul eventually did spend a considerable amount of time in Ephesus. Asia is a really big province. It's hardly inconceivable that Peter could have spent time in Asia without spending much if any time in Ephesus. That said, there is in fact some evidence that there was a very small Christian community in Ephesus before Paul (cf. 18:18-19:7), associated with John (the Baptist, according to Luke, but I've long suspected that Luke has confused his Johns here) rather than Peter. Given that this pre-existent community is associated with a named figure other than Peter I am inclined to think that Peter's time in Asia was spent outside that major city. Rather, I suspect that he traveled by foot from Judea, passing through Cappadocia and likely northern Galatia, before traveling to coastal locales in Pontus, Bithynia, and Asia by ship along the southern the Black Sea. Paul's decision to later set up shop in Ephesus thus makes perfect sense.
My thinking is that during the first and second missionary journeys Paul was focused upon fulfilling Isaiah 66:19. In his mind, it was not necessary that the Word be preached in every corner of the regions that he understood to be named in those passages, but merely that it was preached somewhere in those regions. If he had reason to think that any missionary work took place there, he would skip over the place. Thus does he skip over Cyrene, Asia, Mysia, and Bithynia. By the third missionary journey, he considers Isaiah 66:19 to have been fulfilled, and thus is free to work in regions that he bypassed in his earlier fervour to satisfy prophecy. Thus does he proceed to Ephesus, a very strategic locale that allows him to further his missionary aims in this new phase of activity. The pre-existing Christian community amounts to only a very small number (only around a dozen, perhaps), and Paul perhaps thought that this "other man's foundation" was sufficiently small that he saw Ephesus as basically "virgin" territory. This might also be why Luke emphasizes the heterodoxy (from a Pauline perspective) of their beliefs: this foundation was a bit shaky, and thus needed Pauline refounding. Perhaps Paul then saw the foundation as his own from that point forward. In any case, I've written enough, and I'll leave it there.