"One leak will sink a ship: and one sin will destroy a sinner"

John Bunyan’s words draw a striking parallel between physical vulnerability and moral peril through the analogy of a leaking ship and the condition of the soul. A ship, designed to keep water out and passengers safe, relies on its complete integrity; even a single leak, however small, can let water in, eventually filling the hold and causing the vessel to founder. The fate of that ship, threatened or lost by what seems an insignificant breach, underscores the seriousness of attention to detail and the perils of neglect.

Translating this lesson to the moral life, Bunyan suggests that the soul's well-being requires similar vigilance. Just as a single weakness in a ship may lead to catastrophe, even one cherished or unaddressed fault in a person can undermine their spiritual safety. The use of "one sin" highlights the danger of complacency, entertaining even a single wrong habit or choice leads to spiritual decay, regardless of good intentions or other virtues maintained. It is a call to moral thoroughness, reminding individuals that integrity is not comprised of many good parts coexisting with tolerated evils, but rather of a unified, undivided whole.

Bunyan’s metaphor further carries a sense of inevitability. The unattended leak and unrepented sin share a common end, destruction. Passive tolerance is depicted as dangerous; failing to repair the ship or confess the fault allows ruin to seep in gradually but irresistibly. This provides a sobering warning about the consequences of small compromises or hidden faults. In a broader sense, it encourages personal honesty, humility, and a diligent examination of conscience. Bunyan’s warning is not only about the catastrophic outcome but also about the gradual process by which small, overlooked issues grow into overwhelming threats. Both ship and soul demand constant care, and survival depends on mending each breach, however trivial it might appear at first.