incurvatus in se

The great reformer, Martin Luther, in the Lectures on Romans (1515–1516) gives the depiction of the sinner as incurvatus in se, “curved in on self”:

“due to original sin, our nature is so curved in upon itself at its deepest levels that it not only bends the best gifts of God toward itself in order to enjoy them (as the moralists and hypocrites make evident), nay, rather, "uses" God in order to obtain them, but it does not even know that, in this wicked, twisted, crooked way, it seeks everything, including God, only for itself. As the prophet Jeremiah says in Jer. 17:9: "The heart of man is crooked and inscrutable; who can know it?" i.e., it is so curved in upon itself that no man, be he ever so holy, can know it (apart from a testing experience). As it says in Ps. 19:12: "Who can discern his errors? Clear thou me from my hidden faults!"