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. For which cause also I have been much
hindered from coming to you. But now having no more place
in these parts, and having a great desire these many years to come unto
you; Whensoever I take my journey into Spain, I will
come to you: for I trust to see you in my journey, and to be brought on
my way thitherward by you, if first I be somewhat filled with your
company. But now I go unto Jerusalem to minister unto the
saints. For it hath pleased them of Macedonia and Achaia
to make a certain contribution for the poor saints which are at
Jerusalem. It hath pleased them verily; and their debtors
they are. For if the Gentiles have been made partakers of their
spiritual things, their duty is also to minister unto them in carnal
things. When therefore I have performed this, and have
sealed to them this fruit, I will come by you into Spain.
And I am sure that, when I come unto you, I shall come in the fulness
of the blessing of the gospel of Christ.
Chrysostom in his Homily 29 says regarding v.18:
"And none, he means, can say that my words are a mere boast. For of this priestly ministry of mine, the signs that I have, and the proofs of the appointment too, are many…see how violently he tries to show that the whole is God's doing, and nothing his own. For whether I speak anything, or do anything, or work miracles, He does all of them, the Holy Spirit all. And this he says to show the dignity of the Holy Spirit also."
And about v.21 Chrysostom says simply:
"You see he runs to where the labor is more, the toil greater…"