BUT I HAVE WRITTEN VERY BOLDLY TO YOU ON SOME POINTS: tolmeroteron de egrapsa (1SAAI) humin apo merous: (Hebrews 13:22; 1 Peter 5:12; 1 John 2:12-14; 5:13; Jude 1:3-5)

Have written is epistolary aorist, a device whereby a first-century writer observes the courtesy of putting himself at the viewpoint of the recipient of the letter, viewing the writing of his letter which is a present occurrence to him, as a past event, which latter viewpoint the reader would have when receiving the letter. The reference is therefore to the contents of the letter to the Romans which he was then in the process of writing.

Very boldly (5112) (tolmeros from tolma = courage) pertains to having courage, boldness or confidence. The actual Greek word is the comparative of tolmeros, tomeroteron (Technically = adjective, normal, accusative, neuter, singular, comparative) which means more boldly, rather freely, a little boldly, with greater confidence and freedom and describes one particularly bold and daring.

Vincent says,

Not too boldly, but the more boldly because you are full of goodness.

Stedman makes an interesting comment...

Now, you would think that a church that was theologically knowledgeable, able to instruct and counsel one another in the deep problems of life, and filled with a spirit of goodness and compassion, would hardly need anything more said to them. Yet it is to that kind of a church that Paul addressed his letter to the Romans. (from An Adequate Ministry)

I've written you a letter, parts of which are rather bold, as a reminder to you.

Phillips renders it...

I have written to you with a certain frankness to refresh your minds with truths that you already know.

Stedman observes:

"In a sense, everyone who reads the letter to the Romans is taking a self-examination of his own spiritual effectiveness. I don't think a Sunday goes by but that someone says to me after a message, "You know, you were talking just to me this morning. In fact, I noticed that you kept looking right at me all the time you were talking." I must say that I have no awareness of picking out individuals at all as I am teaching through this book, but this is the phenomena which often occurs when the Spirit of God is taking the truth and bring it right home to the heart. You can't listen to the book of Romans honestly and openly without having this sense of being under examination yourself. I am sure that these first recipients of this letter had that feeling as the letter was read in the gathering in Rome." (Read full text - The Minister of Jesus Christ)

SO AS TO REMIND YOU AGAIN: os epanamimneskon (PAPMSN) humas: (1 Timothy 4:6; 2 Timothy 1:6; 2:14; Titus 3:1; 2 Peter 1:12-15; 3:1,2)

This was what Peter did as well (see notes 2 Peter 1:12; 2 Peter 3:1; 3:2). A good teacher must keep in mind the opposing problems of familiarity and forgetfulness. Even for the best of minds with the sincerest devotion, that which is not kept familiar eventually will be forgotten.

Stedman comments:

"I saw a man the other day with a string around his finger. The string was to remind him of something. The fact that we so easily forget things is somehow built into our humanity and I think one of the greatest proofs of the fall of man is that we have such a hard time remembering what we want to remember, yet we so easily remember what we want to forget!... Living out in the world, as many of you are, working every day among non-Christians, it is so easy to be sucked into the attitudes of the world around. It is so easy to get the idea that life is designed to be a pleasant picnic, that we can work toward the day when we can retire and enjoy ourselves. I find that attitude prevalent among people everywhere, but that is not what the Bible says. The Bible says we are in the midst of a battle, a battle to the death, against a keen and crafty foe. He wants to discourage us and defeat us, and to make us feel angry and hostile. He knows how to do it, and he never lets up. This life is not designed to be a time of relaxing. There are times when we need recreation and vacations, when we can slow down a bit. But you never see the Apostle Paul talking about quitting the battle. You cannot quit, as long as life is there. So Paul tells us that we need to be reminded, day by day and week by week, that we are in a battle and that we have a crafty foe. This life is not all there is, by any means. This is school time, a training ground, where we are to learn our lessons. This life is getting us ready for the real thing that is yet to come." (Click full sermon)

BECAUSE OF THE GRACE OF GOD THAT WAS GIVEN TO ME FROM GOD: dia ten charin ten dotheisan (APPFSA) moi hupo tou theou: (Ro 1:5 12:3,6 1Cor 3:10, 15:10)

Grace (5485) (see word study charis)

Was given is aorist tense, which speaks of his receipt of this gift of grace at some point in time, specifically corresponding undoubtedly with his being set apart for the gospel (see note Romans 1:1, 1:5 cf Act 9:1-16) could explain why Paul considers himself a debtor or under obligation (see note Romans 1:14).

TO BE A MINISTER OF CHRIST JESUS TO THE GENTILES: eis to einai (PAN) me leitourgon Christou Iesou eis ta ethne:  (For more insights into Paul's ministry to the Gentiles study the following cross references: 18; 11:13; Acts 9:15; 13:2; 22:21; 26:17,18; 1 Corinthians 3:5; 4:1; 2 Corinthians 5:20; 2 Corinthians 11:23; Galatians 2:7,8; Ephesians 3:1; Philippians 2:17; 1 Timothy 2:7; 2 Timothy 1:11)

Minister (3011) (leitourgos from léïtos = of the people [NIDNTT says it from "laos" = people] + érgon = work) is literally a worker of the people. In classical Greek leitourgos referred especially to persons performing public duties, or works of public use.

Kenneth Wuest explains that "minister" in this verse is not

the usual word... diakonos (servant), but leitourgos , used in secular life of a public minister, a servant of the state, in sacred things, of the priests of the Jerusalem Temple [Ed: used to describe the work of Christ our "Great High Priest in (Heb 8:2)]. Another source says this word originally meant someone who does public service at his own expense, but in Christian literature it came to be used of the service of god (cf same word translated "servants" - see note Romans 13:6) Paul uses it here to speak of his ministry of preaching the gospel as a priestly ministry & of equal value and sacredness to the ministry of the priesthood of the OT." Thus the Christian ministry is seen as a priestly ministry which parallels Peter's teaching on who believers are in (see notes 1Peter 2:5,1Peter 2:9). In the Septuagint   leitourgos was used in translating a technical term for priestly service to God. Luke employed the verbal form (leitourgeo [3008]) to describe the ministry of Paul and Barnabas at the church of Antioch (Acts 13:2). It was also used of the ministry of the Macedonian and Achaian Christians who gave to the poor in Jerusalem (Romans 15:27). Paul used the noun (leitourgos) in (note Philippians 2:25) for the ministry of Epaphroditus to the Philippian saint. (Wuest, K. S. Wuest's Word Studies from the Greek New Testament: Studies in the Vocabulary of the Greek New Testament: Grand Rapids: Eerdmans)

Hughes adds that..
 

"Paul could have used other words to describe himself. For example, he could have used the common term doulos to indicate a servant of Jesus Christ, or he could have used diakonos, which means “servant” or “minister.” But he chose leitourgos because he saw his missionary work like that of a priest offering sacred worship to God. Consonant with this, he saw his priestly offering not as a lamb or a grain offering, but as Gentile converts. As he expresses it in v16: “that the Gentiles might become an offering acceptable to God, sanctified by the Holy Spirit.” Here we are exposed to Paul’s remarkable self-conception. Though he is involved in the dusty, mundane business of traveling the ancient world on foot, suffering from exposure, threats, beatings, and rejection, in his heart of hearts he sees himself in priestly garb in the Temple, lifting up the souls of men which then ascend as a sweet-smelling fragrance to Christ. Fully apprehended and appreciated, this is a dazzling picture." (Hughes, R. K. Romans: Righteousness from heaven. Preaching the Word. Wheaton, Ill.: Crossway Books)

MINISTERING AS A PRIEST THE GOSPEL OF GOD: hierourgounta (PAPMSA) to euaggelion tou theou:  (29; 1:1; Acts 20:24; Galatians 3:5; 1 Thessalonians 2:2,9; 1 Timothy 1:11; 1 Peter 1:12)

Ministering as a priest  (2418) (hierourgeo)  is used in the unusual way of referring to Christian service but not in connection with any liturgical practice but explicitly with the gospel of God. It is a striking way of affirming that the proclamation of the gospel originates with God and is "sacred".

Vines says "ministering as a priest" means

“to minister in priestly service” (from hieros [2413] sacred [24x in Acts] + ergon [2041] work) [and] is used by Paul metaphorically of his ministry of the Gospel. The offering connected with his priestly ministry is “the offering up of the Gentiles,” i.e., the presentation by Gentile converts of themselves to God."

(Vine, W. Collected writings of W. E. Vine. Nashville: Thomas Nelson )

Paul took very seriously his call to minister to the Gentiles (cf Rom 11:13, Gal 2:9). He never renounced his Jewish heritage, but on the other hand he was faithful to be God's minister to the Gentiles (cf Acts 22:21).

Denney explains,

“The offering which Paul conceives himself as presenting to God is the Gentile Church, and the priestly function in the exercise of which this offering is made is the preaching of the gospel.”

THAT MY OFFERING OF THE GENTILES MIGHT BECOME ACCEPTABLE SANCTIFIED BY THE HOLY SPIRIT: hina genetai (3SAMS) e prosphora ton ethnon euprosdektos, hegiasmene (RPPFSN) en pneumati hagio: (Ro 12:1,2; Isaiah 66:19,20; 2 Corinthians 8:5; Philippians 2:17; 4:18; Hebrews 13:16; 1 Peter 2:5) (Ro 5:5; 8:26,27; Acts 20:32; 1 Corinthians 6:19; Ephesians 2:18,22; 1 Thessalonians 5:23)

Gentiles are genitive of apposition, which means that the Gentiles themselves constitute the offering! What an “offering” that God wanted Paul to make: the offering of the Gentiles, of human lives. God wanted Paul to bring people to Him.

Offering (4376) (prosphora from prós = toward, before + phéro  = bring) literally means to bring before and not surprisingly is used most often in Hebrews which emphasizes Jesus the High Priest of our confession (other uses in Ac 21:26, Acts 24:17)

Prosphora is used in the Septuagint (LXX = Greek translation of the Hebrew OT) for the sacrifice offered on the altar and it means to carry or bring something or someone into the presence of another usually implying a transfer to the latter individual.

Prosphora thus clearly was part of the vocabulary of priestly worship and in the NT it was used of Christ’s sacrificial offering (Eph 5:2 Heb10:10 of His body).

Compare the similar idea of the presentation of the redeemed believer's body back to God (Who owns it anyway) as a living sacrifice (Ro 12:1-12).

In this verse Paul explains that his purpose for ministering the gospel of God was in order that the Gentiles might actually come to be an acceptable offering (to God) having been set apart from the profane world and unto a holy God by the sanctifying work of the Holy Spirit.

Acceptable (2144) (euprosdektos -- see note Romans 15:31, note  1Pe 2:5, 2Cor 6:2) means well-accepted and conveys a strong affirmation of acceptability.

The OT knew of sacrifices that God would not accept (cf Isa 1:11ff) and Paul is distancing the offering of the Gentiles from such "worthless" offerings.

Compare to "acceptable" offering of our living sacrifice in (Romans 12:1) (note) and the "acceptable" will of God (Romans 12:2) (note). And they were "acceptable" because they were sanctified by the Holy Spirit.

What a radical transformation the gospel had worked in Paul mind. Before conversion he regarded the Gentiles as "unclean", but now he says they are sanctified or set apart! God's Spirit had taken the "unclean" vessels and made them "holy" vessels (saints).

Note that all three members of the Godhead are mentioned in this verse in the work of salvation.

Sanctified (37) (hagiazo cf study on related hagios) (most often in Hebrews) and in simple terms means to devote something to the intended purpose for which it was made. Click for a more in depth discussion of the interrelationship of justification (past tense sanctification), sanctification (ongoing salvation), and glorification. 

Ray Stedman has an interesting explanation of sanctified writing that when...

You sit on a chair and you sanctify it; you use it for the purpose it was intended for. When you play an organ, you sanctify it; an organ was intended to be played. You don't attempt to type a letter with it -- that would be to use it in an unsanctified way -- but you play it. When you sanctify your shoes, you put them on your feet; that is what they were intended for. This is the simple meaning for sanctification" to put to the intended use." "You are not your own ..." -- you were never made to be your own, and, if you think you are your own and can run your own life, you are defeating the purpose for which you were created. "You are not your own, you are bought with a price." Therefore, acceptable service is simply to allow yourself to be available and at the disposal of the One who has the right to use you as he pleases, in the place that he pleases, and under the conditions that he chooses. That is being sanctified by the Holy Spirit." (Read full sermon The Minister of Jesus Christ)

Stedman goes on to add