St. Thomas Aquinas
“Sin is the spiritual death of the soul. Hence man is preserved from future sin in the same way as the body is preserved from future death of the body: and this happens in two ways. First of all, in so far as man’s nature is strengthened inwardly against inner decay, and so by means of food and medicine he is preserved from death. Secondly, by being guarded against outward assaults; and thus he is protected by means of arms by which he defends his body.”
Source: St. Thomas Aquinas, Summa Theologica