Among the “patristic” authorities that Augustine invokes near the end of his anti-Pelagian work De natura et gratia is a couplet from Ambrose’s hymn, “Iam Surgit Hora Tertia.” While these lines have been cited as evidence of the hymn’s authenticity, few have examined their function and meaning in the context of the treatise. I argue that the lines illustrate Augustine’s distinctive use of authorities in De natura et gratia and that this use is driven by two primary motives: first, Augustine (...) wants to counter Pelagius’s use and citation of authorities in Pelagius’s work De natura; and, second, Augustine wants to advance his own views on the necessity of the grace of Christ. Turning to “Iam Surgit,” I first show that Augustine seeks to counter a potential Pelagian “abuse” of the hymn, and especially the way the Pelagians might exploit its reference to “merit.” I then speculate that Augustine uses the hymn to offer implicit support for his own understanding of grace since, according to his reading, the source of forgiveness in Ambrose’s hymn is the gratia Christi. Augustine thus shows not only that Ambrose’s words are media, that is, equally supportive of both sides in the dispute, but also that they advance Augustine’s developing views on the priority of the grace of Christ in the prayers of humanity. (shrink)