Romans 15:17-21 — I have therefore whereof I may glory through Jesus Christ in those things which pertain to God.
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,
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.
Yea, so have I strived to preach the gospel, not where Christ was named, lest I should build upon another man's foundation:
But as it is written, To whom He was not spoken of, they shall see: and they that have not heard shall understand.
Paul takes satisfaction that his ministry is in Christ and about God.
sign = token or indication — it expresses a purpose and appeals to understanding
wonder = something exceptional that makes the viewer marvel — it appeals to imagination
power — declares the source to be supernatural
Spirit of God — responsible for signs and wonders and Paul's preaching (verse 18)
Quote in verse 21 is from Isaiah 52:15 (in the Septuagint) — … for that which had not been told them shall they see; and that which they had not heard shall they consider.
I think that God let Paul's plans go awry and his hopes fail, in order to give great comfort to believers of all generations. If the great apostle could form plans that seemed most holy and most spiritual, most unselfish and most desirable, only to see them fail, shall we not expect that our plans, too, may fail? The Christian who grieves over broken plans does not comprehend the sovereignty of God. But he who says, "It is all right, Lord; do whatever you please with me and mine," is the Christian who is filled with joy. — Donald Grey Barnhouse, God's Glory, page 101.