John Calvin Commentary 1 Corinthians 7:17

"Only, as the Lord hath distributed to each man, as God hath called each, so let him walk. And so ordain I in all the churches." — 1 Corinthians 7:17 (ASV)

Unless everyone, according as God has dispensed His grace, etc. Such is the literal meaning; I have only, in my rendering, used the nominative so that the connection may be easier and more natural. The meaning is: “What, then, is to be done, unless that everyone walk according to the grace given to him, and according to his calling?”

Let everyone, therefore, labor for this, and strive to do good to his neighbors, and, especially, when he should be prompted to it by the particular duty of his calling.” He mentions two things: the calling and the measure of grace. These he desires us to consider when deliberating on this matter, as it should be no small stimulus to us to do our duty that God condescends to make us ministers of His grace for the salvation of our fellow believers. The calling, on the other hand, should hold us, as it were, under God’s yoke, even when an individual feels his situation is an unpleasant one.

And so in all the Churches. I believe that he added this in order to counter the slander of some who boasted that he assumed more authority over the Corinthians than he ventured to do over others. At the same time, he might also have had another purpose: that this doctrine might have greater weight when the Corinthians understood that it was already proclaimed in all the Churches. For we embrace more readily what we understand we have in common with all the godly. The Corinthians, on the other hand, would have found it hateful to be bound more strictly than others.