Leo the Great, Sermo XXXIX:
“Therefore, my most estimable audience, if we are to have the power to overcome all of our enemies, let us seek divine assistance through the observance of divine commands, knowing that we can not otherwise gain the advantage of our adversaries, unless we first gain the advantage over ourselves. For there are many sources of contention among us, and the flesh seeks one thing against the spirit, while the spirit seeks another against the flesh. In this contest, if the desires of the body are more powerful, the soul will lose its proper dignity, and it will be extremely dangerous to serve that which we should have commanded. If on the other hand the mind, under the authority of its rector and delighted by the gifts of heaven will trample underfoot the incitements of terrestrial pleasure, and if it will prohibit sin from ruling in its mortal body, then reason will hold the most well-ordered reign, and no illusions of spiritual idleness will make its fortifications totter: that is true peace and liberty for humans, when the flesh is ruled by the spirit as its judge, and the spirit is guided by God as its guardian.”
Quapropter, dilectissimi, ut omnes hostes nostros superare valeamus, per observantiam coelestium mandatorum divinum quaeramus auxilium, scientes non aliter nos praevalere posse adversariis nostris, nisi praevaluerimus et nobis. Sunt enim intra nosmetipsos multa certamina, et aliud caro adversus spiritum, aliud adversus carnem spiritus concupiscit (Galat. V, 17). In qua dissensione si cupiditates corporis fuerint fortiores, turpiter animus amittet propriam dignitatem, et perniciosissimum erit eum servire quem decuerat imperare. Si autem mens rectori suo subdita, et supernis muneribus delectata, terrenae voluptatis incitamenta calcaverit, et in suo mortali corpore regnare peccatum non siverit (Rom. VI, 12), ordinatissimum tenebit ratio principatum, et munitiones ejus nulla spiritalium nequitiarum labefactabit illusio: quia tunc est vera pax homini et vera libertas, quando et caro animo judice regitur, et animus Deo praeside gubernatur.