John Calvin Commentary Romans 15:27

"Yea, it hath been their good pleasure; and their debtors they are. For if the Gentiles have been made partakers of their spiritual things, they owe it [to them] also to minister unto them in carnal things." — Romans 15:27 (ASV)

And their debtors they are, etc. Everyone perceives that what is said here of obligation is said not so much for the sake of the Corinthians as for the Romans themselves; for the Corinthians or the Macedonians were not more indebted to the Jews than the Romans. And he adds the ground of this obligation — that they had received the gospel from them; and he takes his argument from the comparison of the less with the greater. He also employs the same argument in another place: that is, it should not have seemed to them an unjust or grievous compensation to exchange carnal things, which are of immensely less value, for spiritual things (2 Corinthians 9:11). And it shows the value of the gospel when he declares that they were indebted not only to its ministers but also to the whole nation from which the gospel had come forth.

And mark the verb λειτουργῆσαι, to minister; which means to discharge one's office in the commonwealth and to undergo the burden of one's calling: it is also sometimes applied to sacred things. Nor do I doubt that Paul meant that it is a kind of sacrifice when the faithful gave of their own to relieve the needs of their fellow believers; for they thus perform the duty of love that they owe and offer to God a sacrifice of an acceptable odor. But in this place, what he specifically had in view was the mutual right of compensation.