Liberalism is a mortal sin. But Catholic theology teaches us
that all sins are not equally grave, that there is even a
distinction of degree in venial sins. There are also degrees in
the category of mortal sin, (27) just as there are in the
category of meritorious works. The gravity of sin is determined
by the object at which it strikes. Blasphemy, for instance, which
directly attacks God Himself, is a sin of much graver character
than theft, which directly attacks man. With the exception of
formal hate against God, which constitutes the deadliest of all
sins and of which the creature is rarely culpable unless he be in
Hell, the gravest of all sins are those against faith. The reason
is evident. Faith is the foundation of the supernatural order,
and sin is sin in so far as it attacks this supernatural order at
this or the other point; hence that is the greatest sin which
attacks this order at its very foundations. To destroy the
foundations is to destroy the entire superstructure. To cut off
the branch of a tree will not kill it; but to lay the ax to the
trunk or the roots is fatal to its life. Henceforth it bears
neither blossom nor fruit. St. Augustine, Cited by St. Thomas,
characterizes sin against faith in these words: Hoc est peccatum
quo tenentur cuncta peccata. "This the sin which comprehends
all other sins."

The Angel of the Schools expresses himself with his usual
clearness on this point: "The gravity of sin is determined
by the interval which it places between man and (28) God; now sin
against faith, divides man from God as far as possible, since it
deprives him of the true knowledge of God; it therefore follows
that sin against faith is the greatest of all sins."

When sin against faith is simply a culpable privation of the
knowledge of God, it has not the same gravity as a direct and
formal attack upon dogmas expressly defined by revelation. In
this latter case sin against faith, so grave in itself, acquires
that degree of gravity which constitutes heresy. It then contains
all the malice of infidelity, and becomes an express protestation
against the teachings of faith or an express adhesion to a
teaching which is condemned as false and erroneous by the faith
itself. Besides the deadly sin against faith itself, it is
accompanied by hardness of heart, obstinacy, and the proud
preference for one's own reason over the reason of God Himself.

Hence heretical doctrines, and works inspired by them,
constitute the greatest of all sins with the exception of the
formal hate against God, of which only the demons in hell and the
damned are capable. Liberalism then, which is heresy, and all the
works of Liberalism, which are heretical works, are the gravest
sins known in the code of the Christian law. (29)

Liberalism is, therefore, a greater sin than blasphemy, theft,
adultery, homicide, or any other violation of the law of God,
save in such case as where one acts in good faith, in ignorance,
or thoughtlessly.

It is true that modern naturalism does not so regard or
understand the case. But the law of the Church in matters of
morals and doctrine is unchangeable; it ordains today as it did
yesterday, and heresy is always heresy no matter what the shape
it takes. Appearances may be fair, and the devil may present
himself as an Angel of light. The danger is the greater as the
outward show is more seductive. Heresy has never been so
insidious as under its present form of Liberalism. Its range is
so wide that it touches upon every note in the scale, and finds
an easy disguise in its protean facilities. But its most fatal
shaft is in its plea for "liberty of mind." This in its
own eyes is its cardinal virtue. "Intellectual freedom from
dogmatism" is its boast, a boast in reality the mask of
ignorance and pride. To meet such an enemy requires no ordinary
courage guarded by a sleepless vigilance. When encountered it is
obligatory upon the Catholic conscience to resist it with all the
powers of the soul. Heresy and all its works are sins; Liberalism
is the root of heresy, the tree of evil in whose branches (31)
all the harpies of infidelity find ample shelter; it is today the
evil of all evils.