Just as we have descended to this evil state through one man who sinned, so through one man (who is also God) who justifies us we shall ascend that height of goodness.
No one should be confident that he has passed over from the one state to the other, until he has arrived where there will be no more temptation – until he has achieved that peace which is his aim in the many varied struggles of this present warfare, in which ‘the desires of the body oppose the spirit, and the spirit fights against the body’s desires.’
Now this war would never have been if human nature had, by free choice, persisted in that right condition in which it was created. As it is, however, human nature has refused to keep that peace with God in happiness; and so in its unhappiness it is at war with itself.
And yet this evil state is better than the earlier condition of this life; for it is better to struggle against vices than to be free from conflict under their domination. Better war with the hope of everlasting peace than slavery without any thought of liberation.
Our desire is, indeed, to be free even of this war; and by the fire of divine love we are set on fire with longing to attain that orderly peace where our lower parts may be subdued to the higher in a stability that can never be shaken.
But even if (perish the thought!) there were no hope of attaining this great good, we ought none the less to prefer to continue in this state of conflict, with all its troubles, than to allow our vices to have dominion over us by ceasing to resist.
-St. Augustine, The City of God, Book XXI, chapter 15