This article examines how the "erected wit" and "infected will" of Philip Sidney's Defence of Poesie transfigured the classical concept of akrasia—weakness of will, or acting against one's better judgment—for reformed ends, and how this infection of the will (synonymous, for reformers, with the heart) plays out in Sidney's love poetry. Paul's Epistle to the Romans and Ovid's Medea were juxtaposed repeatedly in reformed commentaries on akrasia. As Sidney positioned his Astrophel at the intersection between right reason and human frailty, looking as much like Medea as like Paul ("I see, my course to lose myself . . . I see: and yet" [Astrophel and Stella, sonnet 18]), he felt obliged—by virtue of his conviction that poetry serves didactic ends—to distinguish Astrophel from the pre-Christian reprobate. Self-knowledge about his postlapsarian corruption, resonant of Paul's self-diagnosis in Romans, becomes Astrophel's dominant characteristic as he replays the Fall throughout the sequence. The lover thus confirms reformed claims that self-knowledge—a concept so crucial to Sidney—is the very precondition for grace. By stressing Astrophel's Pauline-rather-than-Medean character, Sidney could more confidently offer his poetic persona as an example of the kind of instructive value he claims poetry possesses—even if Astrophel and Stella serves only to remind its readers that we are perpetually sinning "after the like maner of Adam" (Rom. 5:14).