Look at the verses before and after those which you quoted:
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 [u]For I will not dare to speak of any of those things which Christ hath not wrought by me[/u], 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. 22 For which cause also I have been much hindered from coming to you. 23 But now having no more place in these parts, and having a great desire these many years to come unto you; 24 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 [i]company[/i]. 25 But now I go unto Jerusalem to minister unto the saints. 26 For it hath pleased them of Macedonia and Achaia to make a certain contribution for the poor saints which are at Jerusalem.
Remember that Paul is being very careful within his own ministry, to respect other brethren, many of whom were born again long before him. Likewise, although he could feel justified in being supported by the churches, he prefers to earn his own way, so that no-one can resent him during his long stays to teach in various places (1 Cor 9). I think in these ways he shows his real change of heart.
In mentioning Isaiah's prophecy about the Gentiles being saved, I believe he is quoting it here to explain that he is part of the fulfilment of that prophecy. We know that Peter was first to speak to the Gentiles (Acts 10), but Paul knew God had called him specifically to preach to Gentiles, Jews and kings (Acts 9).
Recently, I came across the verse where God seems to be saying specifically, for the first time, that as a punishment for Israel's waywardness, He is going to make Israel [u]unable[/u] to see or hear - Isaiah 29:10. Consequently, it is less of a surprise when He starts to promise vision and hearing to the Gentiles.
Are these thoughts in any way helpful?
