grace.

_On the contrary,_ Augustine says (De Perfect Just. xxi): "Whoever
denies that we ought to say the prayer 'Lead us not into temptation'
(and they deny it who maintain that the help of God's grace is not
necessary to man for salvation, but that the gift of the law is
enough for the human will) ought without doubt to be removed beyond
all hearing, and to be anathematized by the tongues of all."

_I answer that,_ We may speak of man in two ways: first, in the state
of perfect nature; secondly, in the state of corrupted nature. Now in
the state of perfect nature, man, without habitual grace, could avoid
sinning either mortally or venially; since to sin is nothing else
than to stray from what is according to our nature--and in the state
of perfect nature man could avoid this. Nevertheless he could not
have done it without God's help to uphold him in good, since if this
had been withdrawn, even his nature would have fallen back into
nothingness.

But in the state of corrupt nature man needs grace to heal his nature
in order that he may entirely abstain from sin. And in the present
life this healing is wrought in the mind--the carnal appetite being
not yet restored. Hence the Apostle (Rom. 7:25) says in the person of
one who is restored: "I myself, with the mind, serve the law of God,
but with the flesh, the law of sin." And in this state man can
abstain from all mortal sin, which takes its stand in his reason, as
stated above (Q. 74, A. 5); but man cannot abstain from all venial
sin on account of the corruption of his lower appetite of sensuality.
For man can, indeed, repress each of its movements (and hence they
are sinful and voluntary), but not all, because whilst he is
resisting one, another may arise, and also because the reason is not
always alert to avoid these movements, as was said above (Q. 74, A.
3, ad 2).

So, too, before man's reason, wherein is mortal sin, is restored by
justifying grace, he can avoid each mortal sin, and for a time, since
it is not necessary that he should be always actually sinning. But it
cannot be that he remains for a long time without mortal sin. Hence
Gregory says (Super Ezech. Hom. xi) that "a sin not at once taken
away by repentance, by its weight drags us down to other sins": and
this because, as the lower appetite ought to be subject to the
reason, so should the reason be subject to God, and should place in
Him the end of its will. Now it is by the end that all human ac