A good deal has been made in the scholarship of the significance of the medieval formula, Facientibus quod in se est Deus non denegat gratiam. Often the idea that God will not deny grace to those who do what is in them has been taken as a clear indication of soteriological synergism. One complaint against the formula was that it introduced an element of doubt into the question of salvation. If salvation is dependent upon human effort, one might be tempted to wonder constantly, “Am I working hard enough?”
As David Steinmetz has observed, however, in reference to the facientibus, “To use this axiom commits the user to no particular school of theology.” As I outline in Covenant, Causality, and Law, in the context of covenant you can find similar sorts of dynamics, if not textual constructions or employment of medieval formula, in Augustine, Musculus, and Calvin. They do not necessarily have the technical application of referring to justification, for instance, but they do have some significant implications for the relationship between general and special grace.
Perhaps in some continuity with a covenantal construal of the facientibus, Luther in his 1522 treatment of “The Estate of Marriage” uses something like it to offer comfort to those who are wary of wedlock out of worry “of being poor and despised, and doing insignificant work.” To the latter concern, Luther says that the “status and occupation” of marriage “are pleasing to God.” But in relation to the former worries about material well-being, Luther adds these words of comfort and exhortation to the potential husband: “God will most certainly provide for him if only he does his job to the best of his ability.”
Luther’s use of the facientibus makes clear that there is a kind of providential promise attached to God’s expectations for obedient execution of one’s vocational responsibility. The fact, however, that this promise is limited to the mundane and not to the question of soteriology does nothing to undermine Oberman’s conclusion that “not merely the ‘young Luther,’ but already the ‘youngest Luther,’ before beginning his career as a professor, as a biblical exegete, and eventually as a Reformer, has on points which later prove to be cornerstones in the structure of his thought become independent of the nominalistic theological tradition in which he was reared,” including the Pelagian construal of the facientibus.