"Guilt upon the conscience, like rust upon iron, both defiles and consumes it, gnawing and creeping into it, as that does which at last eats out the very heart and substance of the metal"

Bishop Robert South’s comparison of guilt to rust reveals the internal and corrosive nature of a troubled conscience. Guilt is not simply an external burden or a fleeting emotion; rather, it seeps deep within, affecting the very essence of the individual. Just as rust forms slowly on iron, working its way from the surface inward, guilt commences as a subtle discomfort and gradually invades the soul. The metaphor highlights both the contaminating ("defiles") and destructive ("consumes") power of guilt. Rust initially tarnishes the appearance of metal, marking it as tainted, yet over time, it does more than mar the surface, it erodes the strength and integrity of the metal itself.

Similarly, guilt first manifests as stains upon the conscience, but if neglected or unaddressed, it can erode moral fiber and self-worth. The words "gnawing and creeping" bring out the insidious progression of guilt. It does not assault all at once; it advances stealthily, almost imperceptibly, underscoring why unresolved guilt can be so damaging. Just as rust persistently works at the metal, guilt nibbles at the spirit, eroding confidence, peace, and clarity. Eventually, it "eats out the very heart and substance", suggesting total inner collapse. For iron, this means structural failure; for a person, it may mean the loss of self-respect, joy, or hope.

South’s metaphor also stresses that, like iron left to rust, a conscience neglected or unhealed by forgiveness and reconciliation grows weaker and more fragile. In both cases, prevention and intervention, whether by caring for the metal or tending to one’s moral injuries, are essential. The passage urges recognition of guilt's power not just to blemish, but to fundamentally destroy if left unchecked, advocating for active reflection and moral maintenance to preserve the "metal" of one’s character.