Romans 15:20

Yea, making it my aim so to preach the gospel, not where Christ was already named, that I might not build upon another man's foundation; but, as it is written, They shall see, to whom no tidings came, And they that have not heard shall understand.

This is a further point in Paul's legitimate recommendation of himself to the church in Rome, namely, that he had not preached in those areas where others had already preached the gospel, but had sought out the places where the truth had not been taught. Paul had deliberately undertaken to proclaim the gospel of Christ to the entire world which he knew, evidently believing that every city on earth should hear the gospel once before any should hear it repeated. Paul's plan of preaching only to those who had "not heard" was justified by his appeal to Isaiah 52:15, where the glory of the Messiah's extended kingdom was that prophet's theme. This was a wise plan; and, as McGarvey noted:

Had Paul's example been followed what needless overlapping of missionary effort might have been avoided. Sectarianism has caused and committed this sin, and it has been especially reprehensible where it has been done to foster points of difference that are matters of indifference as it is where factions of the same sect compete in the same field.[16]

The manner in which Isaiah's prophecy was fitted to Paul's purpose of quoting it was explained thus by Whiteside:

Till the gospel was preached to them no tidings came to the Gentiles. Paul was sent to open the eyes of the Gentiles to turn them from darkness to light, that they might see (Acts 26:14-20). Hence, those who had never heard were made to understand.[17]

[16] Ibid., p. 539.

[17] Robertson L. Whiteside, A New Commentary on Paul's Letter to Saints in Rome (Denton, Texas: Miss Inys Whiteside, 1945), p. 288.