How those are to be admonished who commit very small but frequent faults, and those who, while avoiding such as are very small, are sometimes plunged in such as are grievous.
(Admonition 34.) Differently to be admonished are those who, though the unlawful things they do are very small, yet do them frequently, and those who keep themselves from small sins, but are sometimes plunged in such as are grievous. Those who frequently transgress, though in very small things, are to be admonished by no means to consider the quality of the sins they commit, but the quantity. For, if they scorn being afraid when they weigh their deeds, they ought to be alarmed when they number them; seeing that deep gulphs of rivers are filled by small but innumerable drops of rain; and bilge-water, increasing secretly, has the same effect as a storm raging openly; and the sores that break out on the members in scab are minute; but, when a multitude of them gets possession in countless numbers, it destroys the life of the body as much as one grievous wound inflicted on the breast. Hence for certain it is written, He that despises small things falls little by little. For he that neglects to bewail and avoid the smallest sins falls from the state of righteousness, not indeed suddenly, but bit by bit entirely. Those who transgress frequently in very little things are to be admonished to consider anxiously how that sometimes there is worse sin in a small fault than in a greater one. For a greater fault, in that it is the sooner acknowledged to be one, is by so much the more speedily amended; but a smaller one, being reckoned as though it were none at all, is retained in use with worse effect as it is so with less concern. Whence for the most part it comes to pass that the mind, accustomed to light evils, has no horror even of heavy ones, and, being fed up by sins, comes at last to a sort of sanction of iniquity, and by so much the more scorns to be afraid in greater matters as it has learned to sin in little ones without fear.
But, on the other hand, those who keep themselves from small sins, but are sometimes plunged in grievous ones, are to be admonished anxiously to apprehend the state they are in; how that, while their heart is lifted up for very small things guarded against, they are so swallowed up in the very gulph of their own elation as to perpetrate others that are more grievous, and, while they outwardly master little ills, but are puffed up inwardly with vain glory, they prostrate their soul, overcome within itself by the sickness of pride, amid greater ills even outwardly. Those, then, who keep themselves from little faults, but are sometimes plunged in such as are grievous, are to be admonished to take care lest they fall inwardly where they suppose themselves to be standing outwardly, and lest, according to the retribution of the strict judge, elation on account of lesser righteousness become a way to the pitfall of more grievous sin. For such as, vainly elated, attribute their keeping of the least good to their own strength, being justly left to themselves are overwhelmed in greater sins; and by falling they learn that their standing was not of themselves, so that immeasurable ills may humble the heart that is exalted by the smallest good. They are to be admonished to consider that, while in their more grievous faults they bind themselves in deep guilt, they nevertheless for the most part sin worse in the little faults which they guard against; because, while in the former they do what is wicked, in the latter they hide from men that they are wicked. Whence it comes to pass that, when they perpetrate greater evils before God, it is a case of open iniquity; and when they are careful to observe small good things before men, it is a case of pretended holiness. For hence it is that it is said of the Pharisees, Straining out a gnat, but swallowing a camel. As if it were said plainly. The least evils you discern; the greater you devour. Hence it is that they are again reproved by the mouth of the Truth, when they are told, You tithe mint and anise and cummin, and omit the weightier matters of the Law, judgment and mercy and truth. For neither is it to be carelessly heard that, when He said that the least things were tithed, He chose indeed to mention the lowest of herbs, but yet such as are sweet-smelling; in order, surely, to show that, when pretenders observe small things, they seek to extend for themselves the odour of a holy reputation; and, though they omit to fulfil the greatest things, they still observe such of the smallest as smell sweetly far and wide in human judgment.
Source: Pastoral Rule (New Advent)