What is the meaning of Romans 1:13-15?

13 Now I would not have you ignorant, brethren, that oftentimes I purposed to come unto you, (but was let hitherto,) that I might have some fruit among you also, even as among other Gentiles. 14 I am debtor both to the Greeks, and to the Barbarians; both to the wise, and to the unwise. 15 So, as much as in me is, I am ready to preach the gospel to you that are at Rome also. (Romans 1:13-15 KJV)

William Burkitt’s Commentary

Here observe, How the apostle blocks an objection and prevents a reflection upon himself: Some at Rome might be ready to say that if Paul had such a longing desire to see us as he expresses, why did he not come all this time and preach here, as he has done at Corinth and Ephesus, and elsewhere? He truly tells them, therefore, that it was not for want of inclination and will, but for want of opportunity; he had often intended it, and attempted it also, but was providentially hindered.

From whence I gather, That the ministers of God cannot always dispose of themselves and their labours according to their own inclinations and desires, but both their persons and ministry are directed and disposed of by the providence, and according to the pleasure of Almighty God.

Observe, 2. The great modesty and condescending humility of our apostle in telling the Romans that though he desired and intended to take this long journey to Rome to preach the gospel to them, yet this was rather a debt than a gift: He does not intimate to them that his coming amongst them was an arbitrary favour for which they should be indebted to him, but a bounden duty which he owed to them;  I am a debtor both to Jew and Greek, and ready to preach the gospel to you that are at Rome also.

Here note, That the debt spoken of is the preaching of the gospel: St. Paul contracted this debt, and laid himself under an obligation to pay it then, (as every minister does now) at his first entering upon the office of the ministry; by virtue of his mission, it was his duty to preach the gospel to all, both to the learned Greeks and unlearned Barbarians.

From whence, learn, That to preach the gospel of Christ, both far and near, with laborious diligence, when regularly called thereunto, is a ministerial debt and duty. We are first indebted to God that sends us forth and we are also indebted to the people we are sent to.

But, oh! how many people are there that would willingly forgive their ministers this debt? but we must tender payment at the time and place appointed, or we can never be discharged, whether the debt is accepted or not.