Q: Whether by Penance One Sin Can Be Pardoned Without Another?

A: On the contrary,
Augustine says in De Poenitentia [*De vera et falsa Poenitentia, the authorship of which is unknown]: "There are many who repent having sinned, but not completely; for they except certain things which give them pleasure, forgetting that our Lord delivered from the devil the man who was both dumb and deaf, whereby He shows us that we are never healed unless it be from all sins."

I answer that,
It is impossible for Penance to take one sin away without another. First because sin is taken away by grace removing the offense against God. Wherefore it was stated in the Second Part (I-II, Q. 109, A. 7; Q. 113, A. 2) that without grace no sin can be forgiven. Now every mortal sin is opposed to grace and excludes it. Therefore it is impossible for one sin to be pardoned without another. Secondly, because, as shown above (A. 2) mortal sin cannot be forgiven without true Penance, to which it belongs to renounce sin, by reason of its being against God, which is common to all mortal sins: and where the same reason applies, the result will be the same. Consequently a man cannot be truly penitent, if he repent of one sin and not of another. For if one particular sin were displeasing to him, because it is against the love of God above all things (which motive is necessary for true repentance), it follows that he would repent of all. Whence it follows that it is impossible for one sin to be pardoned through Penance, without another. Thirdly, because this would be contrary to the perfection of God's mercy, since His works are perfect, as stated in Deut. 32:4; wherefore whomsoever He pardons, He pardons altogether. Hence Augustine says [*De vera et falsa Poenitentia, the authorship of which is unknown], that "it is irreverent and heretical to expect half a pardon from Him Who is just and justice itself."

Reply Obj. 1: These words of Gregory do not refer to the forgiveness of the guilt, but to the cessation from act, because sometimes a man who has been wont to commit several kinds of sin, renounces one and not the other; which is indeed due to God's assistance, but does not reach to the pardon of the sin.

Reply Obj. 2: In this saying of Ambrose "faith" cannot denote the faith whereby we believe in Christ, because, as Augustine says on John 15:22, "If I had not come, and spoken to them, they would not have sin" (viz. unbelief): "for this is the sin which contains all others": but it stands for consciousness, because sometimes a man receives pardon for a sin of which he is not conscious, through the punishment which he bears patiently.

Reply Obj. 3: Although sins are not connected in so far as they turn towards a mutable good, yet they are connected in so far as they turn away from the immutable Good, which applies to all mortal sins in common; and it is thus that they have the character of an offense which needs to be removed by Penance.

Reply Obj. 4: Debt as regards external things, e.g. money, is not opposed to friendship through which the debt is pardoned; hence one debt can be condoned without another. On the other hand, the debt of sin is opposed to friendship, and so one sin or offense is not pardoned without another; for it would seem absurd for anyone to ask even a man to forgive him one offense and not another.

Reply Obj. 5: The love whereby God loves man's nature, does not ordain man to the good of glory from which man is excluded by any mortal sin; but the love of grace, whereby mortal sin is forgiven, ordains man to eternal life, according to Rom. 6:23: "The grace of God (is) life everlasting." Hence there is no comparison.