The Institutes, Book 1
The Spiritual Belt and Its Hidden Meaning
Dressed, then, in these garments, the soldier of Christ should know first of all that he is protected by the belt tied around him. It is there not only so that he may be ready in mind for all the work and business of the monastery, but also so that he may always go about unhindered by his dress. For the more earnest he is in his zeal for obedience and work, the more ardent he will prove to be in purity of heart, for spiritual progress and the knowledge of divine things. Second, he should realize that in the very wearing of the belt there is no small mystery, declaring what is required of him. For girding the waist and binding it around with a dead skin signifies that he carries about the putting to death of those members in which the seeds of lust and lewdness are contained. He always knows that the command of the gospel, “Let your waist be girded,” applies to him as the apostle interprets it: “Put to death your members that are on the earth: sexual immorality, impurity, lust, evil craving.”
So we find in Holy Scripture that only those wore the belt in whom the seeds of fleshly lust are found to have been destroyed, and who sing with all their might these words of blessed David: “For I have become like a wineskin in the frost.” For when the sinful flesh is destroyed in their inmost parts, they can stretch out the dead skin of the outward man by the power of the spirit. And so he adds, with meaning, “in the frost.” For they are never satisfied merely with putting the heart to death. They also have the impulses of the outward man, and the urges of nature itself, frozen from without by the coming of the frost of self-control. This is so, provided that, as the apostle says, they no longer allow sin to reign in their mortal body, and no longer carry a flesh that resists the spirit.