Why was every place Paul went virgin territory?
The Twelve apostles confined their ministry to the nation of Israel and had no outreach beyond it. Therefore Paul could not build on another man's foundation. He preached the gospel in regions beyond, where no prior apostolic work existed, making every place virgin territory for his apostolic ministry.
Les explains that the Twelve apostles, under the Lord's earthly ministry, had no ministry outside the nation of Israel; they seldom went beyond the Jordan River. So when Paul went to Corinth, Athens, Ephesus, or Asia Minor, he was not building on another man's line. He hoped that as the faith of the Corinthians increased, he could be enlarged to preach the gospel in the regions beyond them—Rome, Spain, Great Britain, and eventually the New World. Because the Twelve had not covered the Mediterranean area, every place Paul went was virgin territory, all because of his authority as an apostle.