“How is it possible for such a faith to be active in love, i.e., in works toward our neighbors on earth?” “Why does this faith willingly descend to the realm which is otherwise ruled by law, the realm of works, the earthly kingdom?” Some say Luther never satisfactorily answered these questions, according to Gustaf Wingren in Luther on Vocation.
“Luther has affirmed that faith and love hang together, but he has never demonstrated it,” says one critic. “Serious consequences followed from the theoretical lack of a systematic relationship between justifying faith and the fulfillment of vocation in the service of love,” says another. Luther is satisfied with the “affirmation that the one cannot be without the other,” but “the necessary inner unity between faith and the power proceeding therefrom for action in vocation Luther has not been able to establish.”
Wingren answers for Luther as follows. “In him who has received the gospel in his heart, there dwells love for his neighbor, a fact at which he is surprised.” “If Luther had shown by logical principles how faith must express itself in love,” “he would have replaced the reality of God with an intellectual construction and denied the miraculous character of something which is a miracle.” “That faith is coupled with love is in fact the same miracle as that in which God became man.” “Faith is the divine nature of works and it is poured out in works even as in Christ the divine nature is poured out in the human.” “When faith works in love, it descends and is incarnated, as God became man in Christ.”
Put differently, that faith expresses itself in love through vocation is as much a miracle as the incarnation of God in Christ Jesus.