Hypocrisy

151. Hypocrisy is a vice by which we affect to demonstrate externally a virtue and a sanctity which we do not possess; and he is really a hypocrite who, being full of wickedness within, pretends in his outward appearance to be good.
There is no vice against which Jesus Christ has inveighed so much in His Gospel as against this one [Matt. vi, 7, 15, 21], condemning it with eight cries of "Woe unto you," which are eight maledictions. And St. Gregory remarks that the hypocrites, blinded by pride and hardened in their sins, generally die impenitent without ever being enlightened, for a reason which is perhaps taken from St. Peter Chrysologus, because while we can see that the remedies to the amendment of other vices do good, the disease of hypocrisy is so pestilential that it affects the very remedies themselves, so that they only serve to foment and increase the evil. "Brethren," says the Saint, "this pestilence must be avoided that turns remedies into diseases, medicines into maladies, holiness into vice, saintliness into sinfulness."
Hypocrisy is always a mortal sin when we pretend to be spiritual and holy, and try to appear as such, when we are not so at heart, caring more for the opinion of men than for the opinion of God; and it is worse still when we affect sanctity in order to further our own advancement and to acquire credit in order to reach and to work evil; or else to obtain some honour, or other temporal good.
In this way also we sin gravely by hypocrisy when we show ourselves scrupulous about works of supererogation or in certain minute observances, not fearing at the same time to transgress against the essential duties of religion and our own state of life, "having left the weightier things of the law," like those Scribes and Pharisees whom Christ reproved, saying that they "strain a gnat and swallow a camel." [Matt. xxiii, 24]
Also when in all the functions connected with the service of God we pretend to have a pure intention when we have it not: "And seek to please not God but men, not the conversion but the favour of the people." [D. Th. 2a 2æ, qu. lxi, art. 2]
The fathers generally call hypocrisy perversity, iniquity, impiety; and it is easy not only to fall into this sin, but to become so accustomed to it that it leads us into atheism. We often begin by serving God with a certain degree of holy fervour, but when this diminishes, we no longer serve God but only pretend to serve Him in order to keep up outward appearances. "Woe unto you hypocrites!" [See St. Thomas, 2a 2æ, qu. xi, per tot.]