14 And I myself also am persuaded of you, my brethren, that ye also are full of goodness, filled with all knowledge, able also to admonish one another.
15 Nevertheless, brethren, I have written the more boldly unto you in some sort, as putting you in mind, because of the grace that is given to me of God,
16 That I should be the minister of Jesus Christ to the Gentiles, ministering the gospel of God, that the offering up of the Gentiles might be acceptable, being sanctified by the Holy Ghost.
17 I have therefore whereof I may glory through Jesus Christ in those things which pertain to God.
18 For I will not dare to speak of any of those things which Christ hath not wrought by me, to make the Gentiles obedient, by word and deed,
19 Through mighty signs and wonders, by the power of the Spirit of God; so that from Jerusalem, and round about unto Illyricum, I have fully preached the gospel of Christ.
20 Yea, so have I strived to preach the gospel, not where Christ was named, lest I should build upon another man's foundation:
21 But as it is written, To whom he was not spoken of, they shall see: and they that have not heard shall understand.
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When speaking of his apostolic ministry, Paul does not accidentally emphasize that he never preached where there were already churches founded thanks to the preaching of other witnesses of the Kingdom (vv. 20-21). Evidently, for Paul himself such ministry was a sign that he was bearing witness precisely to Christ and to the Kingdom, and not to his own religion.
Indeed, preaching to those who had already been converted could easily have turned into the preaching of particular ideas and views, all the more when the person involved was as striking in every respect as Paul was. He had plenty to tell besides Christ and the Kingdom. But that would have been possible only if he had preached to those who had already accepted Christ. In that case the apostle really could have begun, as other preachers did, to set out his own views and concepts. But this was exactly what Paul tried with all his strength to avoid, although it is perfectly clear that, had the matter come to concepts, he could have set them out for his listeners in such abundance as no one else could have offered them.
Paul is extremely cautious about instruction and exhortation. He does not seek to become either a teacher or a spiritual guide for those who, as he is convinced, need nothing of the sort (vv. 14-16). He merely reminds the members of the Roman church, as brothers, of what seemed to him fundamentally important for spiritual life.
But evidently this attitude toward his own ministry was important for Paul in another respect as well. He clearly knew how powerful the effect of his witness was and how significant his word was for Christians. Under such circumstances, the mere appearance of the apostle could well have introduced a certain discord into the settled life of a church, where, of course, there were already teachers, guides, and preachers of its own. A person of such stature would inevitably have drawn every eye and all attention to himself in any church, and Paul plainly did not want this at all: for the Kingdom and for witness, such a state of affairs would not have been useful in any way. And the apostle prefers to act where the circumstances themselves will limit his witness exclusively to the theme of Christ and the Kingdom, and where he will in no way be able, even unintentionally, to disturb the life of already existing churches. Just as an apostle should.