Romans 1:14-15b

I am obligated both to Greeks and non-Greeks, both to the wise and the foolish. 15That is why I am so eager to preach the gospel also to you who are at Rome.

(v14-15, NIV)

It is true that in a sense Paul has an obligation to these people because of God's calling. God has called him to preach the gospel to these people. However, that's more with regards to an obligation to God rather than people. There is a more direct and important way in which Paul is debtor to Greeks and barbarians.

The way in which you could come into debt with someone is you could borrow. If you borrow from the bank, you owe the bank some money hoping to pay it back later. If you borrow a shirt from a friend, you owe him his shirt back after you're done borrowing it or after a certain period of time. So, when we receive grace from God, do we come into debt with him? No, it's by grace. If it were to bring us into debt, then it would no longer be grace. Paul is obligated to these people because he has received this grace freely. If he does not willingly share the good news of the gospel to these people, he is essentially saying that he deserves it and they don't. In the same way, if you by chance stumbled across a cure for cancer that was also free, you'd owe it to the other people stricken with cancer to share this cure with them. If you don't, you're essentially saying that you deserve it and they don't. God's free gift of grace is not owed, but we become into debt with people. In this way is Paul in debt to people. He did not receive it based on works and thus he is obligated to share it with others in order to continue to receive this free gift of grace.

Have you received Jesus as your Lord and savior? Are you by grace through faith saved freely regardless of your works? If so, you are obligated to Greeks and to barbarians, to the wise and to the foolish. Tell them and share with them this free gift of grace which you have received.