. . . merciful, as your
Father also is merciful." Now our Lord commanded His disciples to be
merciful by frequently pardoning their brethren who had sinned
against them; wherefore, as related in Matt. 18:21, when Peter asked:
"How often shall my brother off end against me, and I forgive him?
till seven times?" Jesus answered: "I say not to thee, till seven
times, but till seventy times seven times." Therefore also God over
and over again, through Penance, grants pardon to sinners, especially
as He teaches us to pray (Matt. 6:12): "Forgive us our trespasses, as
we forgive them that trespass against us."

_I answer that,_ As regards Penance, some have erred, saying that a
man cannot obtain pardon of his sins through Penance a second time.
Some of these, viz. the Novatians, went so far as to say that he who
sins after the first Penance which is done in Baptism, cannot be
restored again through Penance. There were also other heretics who,
as Augustine relates in _De Poenitentia_ [*De vera et falsa
Poenitentia, the authorship of which is unknown], said that, after
Baptism, Penance is useful, not many times, but only once.

These errors seem to have arisen from a twofold source: first from
not knowing the nature of true Penance. For since true Penance
requires charity, without which sins are not taken away, they thought
that charity once possessed could not be lost, and that,
consequently, Penance, if true, could never be removed by sin, so
that it should be necessary to repeat it. But this was refuted in the
Second Part (II, Q. 24, A. 11), where it was shown that on account of
free-will charity, once possessed, can be lost, and that,
consequently, after true Penance, a man can sin mortally.--Secondly,
they erred in their estimation of the gravity of sin. For they deemed
a sin committed by a man after he had received pardon, to be so grave
that it could not be forgiven. In this they erred not only with
regard to sin which, even after a sin has been forgiven, can be
either more or less grievous than the first, which was forgiven, but
much more did they err against the infinity of Divine mercy, which
surpasses any number and magnitude of sins, according to Ps. 50:1, 2:
"Have mercy on me, O God, according to Thy great mercy: and according
to the multitude of Thy tender mercies, blot out my iniquity."
Wherefore the words of Cain were reprehensible, when he said (Gen.
4:13): "My iniquity is greater than that I may deserve pardon