Let us subject our minds to God, then, if we wish to make our bodies our servants and to triumph over the devil. Faith is what first subjects our minds to God; then come the commandments by which to live, and if we keep them, our hope is strengthened and our love is nourished, and what before was simply believed begins to become clear. Since both knowledge and action make a person happy, then, just as error is to be avoided in our knowing, so wickedness is to be avoided in our actions. Anyone who thinks he can know the truth while he is still living wickedly is mistaken. Wickedness is to love this world and to prize things that are born and pass away, to desire them and to toil to acquire them and to rejoice when they are plentiful, to fear that they will perish, to be sad when they do so. Such a life cannot see that pure and genuine and unchanging truth; it cannot cling to it and no longer be moved for all eternity. Before our minds are cleansed, then, we have to believe what we cannot yet understand, just as was most truly said by the prophet: “Unless you believe, you will not understand,” (Is 7:9, acc. to the LXX). ....
Suckled on simple and genuine faith, let us be nourished in Christ, and while we are children, let us not seek the food of older people, but with healthy nourishment let us grow in Christ by good lives and Christian righteousness which perfects and strengthens the love of God and neighbor, so that each of us, because he has put on Christ, can in himself triumph over the devil-enemy and his angels. For perfect love neither desires nor fears the world, that is, it does not desire to acquire temporal things nor fear to lose them. Those are the two doors through which the enemy enters and rules, and he can be driven out first by the fear of God and then by love of God.
We ought, then, more eagerly to desire the fullest and clearest knowledge of the truth the more we make progress in love, our hearts cleansed by its genuineness. For truth is seen by the inner eye: “Blessed are the pure of heart, for they shall see God (Mt 5:8). “Rooted and grounded in love, let us be able to comprehend, with all the saints, what is the breadth and length and the height and the depth, and to know also the love of Christ that surpasses all knowledge so that we may be filled with all the fullness of God” (Eph 3:17-19). And, after these struggles of ours with our invisible enemy, may we deserve the crown of victory, because to the eager and the loving the yoke of Christ is easy and his burden light (Mt 11:30). (Augustine, On Christian Combat, XIII, 14, 23; XXXIII, 35; PL 40, 299, 310)
The first paragraph above reminds me of a feature of nearly all schools of ancient philosophy that has most recently been stressed by Pierre Hadot: philosophy was considered a way of life and required a person to engage in spiritual exercises, which included a kind of asceticism, in order to become the self-aware person who alone could achieve a true view of the universe. In their own terms they would have agreed with Augustine when he says, “Anyone who thinks he can know the truth while he is still living wickedly is mistaken.” Some type of moral conversion is needed, then, if one is reach the truth about human living and about the external world. I think of how Bernard Lonergan argued that to be a theologian one needed three conversions: religious, moral, and intellectual. While we are tempted to think that the order of these would be, first, intellectual, then moral, and finally religious, Lonergan thought that they commonly occurred in the reverse order: religious conversion prompting moral conversion with intellectual conversion occurring last, and more rarely.
In any case, it raises the question: What is the relationship between living a moral life and reaching the truth?