This verse depends upon the former; and though it doth not seem to appertain to the argument the apostle had in hand, yet, by the direction of the Spirit, he takes the little occasion that is offered, to show, that election and vocation are only by grace, and not by works. This he had spoken to before, Romans 4:4,5 Romans 9:11; but he toucheth upon it again: and here he delivers a truth, which the Jews of old either could not, or would not, understand; i.e. that there is no mixing of the merit of good works and the free grace of God, but one of these doth exclude and destroy the nature of the other; for if election and calling were both of grace and works, (as some that call themselves Christians, as well as the Jews, affirm), then grace is no grace, and works are no works. For whatsoever proceedeth of grace, that cometh freely, and not of debt; but what cometh by merit of works, that cometh by debt; but now debt and no debt, or that which is free, and by desert, are quite contrary things. Therefore to say, that men are elected and called, partly of grace and partly of the merit of foreseen works, that were to put things together that cannot agree, to make debt no debt, merit no merit, works no works, grace no grace; and so, to affirm and deny one and the same thing.
Related Commentaries of Romans 11:6
Romans 11:6
6 And if by grace, then is it no more of works: otherwise grace is no more grace. But if it be of works, then is it no more grace: otherwise work is no more work.