cannot return except he pay
some sort of penal compensation, which restores him to the equality
of justice; so that, according to the order of Divine justice, he who
has been too indulgent to his will, by transgressing God's
commandments, suffers, either willingly or unwillingly, something
contrary to what he would wish. This restoration of the equality of
justice by penal compensation is also to be observed in injuries done
to one's fellow men. Consequently it is evident that when the sinful
or injurious act has ceased there still remains the debt of
punishment.

But if we speak of the removal of sin as to the stain, it is evident
that the stain of sin cannot be removed from the soul, without the
soul being united to God, since it was through being separated from
Him that it suffered the loss of its brightness, in which the stain
consists, as stated above (Q. 86, A. 1). Now man is united to God by
his will. Wherefore the stain of sin cannot be removed from man,
unless his will accept the order of Divine justice, that is to say,
unless either of his own accord he take upon himself the punishment
of his past sin, or bear patiently the punishment which God inflicts
on him; and in both ways punishment avails for satisfaction. Now when
punishment is satisfactory, it loses somewhat of the nature of
punishment: for the nature of punishment is to be against the will;
and although satisfactory punishment, absolutely speaking, is against
the will, nevertheless in this particular case and for this
particular purpose, it is voluntary. Consequently it is voluntary
simply, but involuntary in a certain respect, as we have explained
when speaking of the voluntary and the involuntary (Q. 6, A. 6). We
must, therefore, say that, when the stain of sin has been removed,
there may remain a debt of punishment, not indeed of punishment
simply, but of satisfactory punishment.

Reply Obj. 1: Just as after the act of sin has ceased, the stain
remains, as stated above (Q. 86, A. 2), so the debt of punishment
also can remain. But when the stain has been removed, the debt of
punishment does not remain in the same way, as stated.

Reply Obj. 2: The virtuous man does not deserve punishment simply,
but he may deserve it as satisfactory: because his very virtue
demands that he should do satisfaction for his offenses against God
or man.

Reply Obj. 3: When the stain is removed, the wound of sin is healed
as regards the will. But punishment is sti