‘But I write the more boldly to you in some measure, as putting you again in remembrance, because of the grace that was given me of God, that I should be a minister of Christ Jesus to the Gentiles, ministering the gospel of God, that the offering up of the Gentiles might be made acceptable, being sanctified by the Holy Spirit.'
Nevertheless he does see himself as having a right to address and guide them because he considers that he has been appointed as a kind of ministering-priest by God on behalf of the Gentiles, who constituted the majority of those in the church at Rome. This is why he feels that he can write to them with a measure of boldness reminding them, of his God-given ministry. For just as when the Messiah came He was a ministering-servant (diakonos) of the circumcision (compare Mark 10:45), so now he, Paul, was like a ministering-priest (leitourgos - he uses this word because of the sacrificial connotations that follow, not because he saw himself as a priest) of the Messiah Jesus to the Gentiles, fulfilling the prophecies in Romans 15:9-12. For although Jesus had undoubtedly spoken to many Gentiles in the later part of His ministry as he preached in places like Decapolis (Mark 7:24 to Mark 8:10), His main ministry had been to the Jews. Paul's main ministry on the other hand, on behalf of the Messiah, was to the Gentiles, for he had been officially confirmed as an Apostle (on behalf of the Messiah) to the Gentiles (Galatians 2:8-9).
Paul likens his ministry to the Gentiles on behalf of the Messiah as ‘ministering like a priest' the Good News that has come from God, as he has offered up (as an offering to God) the Gentiles, who have been made acceptable to God through the effectiveness of the Good News, as detailed in Romans 1-11. And they are an offering which has been ‘sanctified (separated off and made holy to God) by the Holy Spirit'. And of course, because they are an offering to God, made holy by the Holy Spirit, they are accepted and received by Him (Romans 14:3). And it is because we are such an offering to God that we as Christians are to offer ourselves up as living sacrifices to God (Romans 12:1). We offer ourselves because we are already an offering made to Him.
Paul thus sees the Temple offerings as having been replaced by the offering to God of all who believe in the Messiah Jesus, in the same way as the Levitical priesthood has been replaced by believers offering their spiritual sacrifices (1 Peter 2:5; Hebrews 13:15), and the Temple seen as God's dwelling place has been replaced by the whole body of true believers (1 Corinthians 3:16; 2 Corinthians 6:16).
‘Because of the grace that was given me of God.' This is the basis of all that he is saying. He is not boasting of himself, but is making clear the ministry that God in His unmerited active favour has bestowed on him, and wrought through him. It was God Who in His grace chose him from his mother's womb for this task (Galatians 1:15; Acts 9:15-16). And it was that task that he had sought faithfully to fulfil.