1) Conversion: “Augustine became a Christian by conversion and not by birth. And in the two great conversions that divide his life into its main periods we today can still clearly discern the real mission and meaning of Christianity. For it is a permanently valid principle that a human being becomes a Christian not by birth but by conversion. Just as the waters of the earth, obeying the law of gravity, naturally flow downward but can be controlled by man’s mind and technology and be made to flow in another direction, so the waters of human existence flow downward of themselves, and only by conversion to faith, hope and love can they be made to flow in the new direction that leads men and women to their authentic stature as human beings.” 
Else where, Ratzinger writes that “belief signifies the decision that at the very core of human existence there is a point which cannot be nourished and supported on the visible and tangible, which encounters and comes into contact with what cannot be seen and finds that it is a necessity for its own existence.
“Such an attitude is certainly to be attained only by what the language of the Bible calls ‘reversal,’ ‘conversion.’ Man’s natural center of gravity draws him to the visible, to what he can take in his hand and hold as his own. He has to turn round inwardly in order to see how badly he is neglecting his own interests by letting himself be drawn along in this way by his natural center of gravity. He must turn round to recognize how blind he is if he trusts only what he sees with his eyes. Without this change of direction, without this resistance to the natural center of gravity, there can be no belief. Indeed belief is the con-version in which man discovers that he is following an illusion if he devotes himself only to the tangible. This is at the same time the fundamental reason why belief is not demonstrable: it is an about-turn… it is a turn that is new every day.”
The Instrumentum Laboris for the “Year of Faith” 2012-2013 begins with the following:
“Increase our faith!”Lk“Have faith in God. Truly, I say to you, whoever says to this mountain, ‘Be taken up and cast into the sea’ and does not doubt in his heart, but believes that what he says will come to pass, it will be done for him. Therefore I tell you, whatever you ask , believe that you have received it, and it will be yours” Mk “Truly, I say to you, if you have faith and never doubt, you will not only do what has been done to the fig tree, but even if you say to this mountain, ‘Be taken up and cast into the sea’, it will be done” Mt
“Because of your little faithMt “Why are you afraid, O men of little faith?” Mt “But if God so clothes the grass of the field, which today is alive and tomorrow is thrown into the oven, will he not much more clothe you, O men of little faith?” Mt Lk “O men of little faith, why do you discuss among yourselves the fact that you have no bread? Do you not yet perceive? Do you not remember the five loaves of the five thousand, and how many baskets you gathered?” Mt
Mt. “But when he saw the wind, he was afraid, and beginning to sink he cried out, ‘Lord, save me!’ Jesus immediately reached out his hand and caught him, saying to him, ‘O man of little faith, why did you doubt?’” Mt “Truly you are the Son of God!”
The Catechism of the Catholic ChurchMt “But I have prayed for you that your faith may not fail; and when you have turned again, strengthen your brethren” Lk “The door of faith”
Augustine’s Three Conversions
“Late have I loved you, O Beauty ever ancient, ever new, late have I loved you! You were within me, but I was outside, and it was there that I searched for you. In my unloveliness I plunged into the lovely things which you created. You were with me, but I was not with you. Created things kept me from you; yet if they had not been in you they would not have been at all. You called, you shouted, and you broke through my deafness. You flashed, you shone, and you dispelled my blindness. You breathed your fragrance on me; I drew in breath and now I pant for you. I have tasted you, now I hunger and thirst for more. You touched me, and I burned for your peace.”
Ratzinger on the Three Conversions:
Thus, (Second Conversion): renouncing a life solely of meditation, Augustine learned, often with difficulty, to make the fruit of his intelligence available to others. He learned to communicate his faith to simple people and thus learned to live for them in what became his hometown, tirelessly carrying out a generous and onerous activity which he describes in one of his most beautiful sermons: "To preach continuously, discuss, reiterate, edify, be at the disposal of everyone - it is an enormous responsibility, a great weight, an immense effort" (Sermon, 339, 4). But he took this weight upon himself, understanding that it was exactly in this way that he could be closer to Christ. To understand that one reaches others with simplicity and humility was his true second conversion.
But there is a last step to Augustine's journey, a third conversion, that brought him every day of his life to ask God for pardon. Initially, he thought that once he was baptized, in the life of communion with Christ, in the sacraments, in the Eucharistic celebration, he would attain the life proposed in the Sermon on the Mount: the perfection donated by Baptism and reconfirmed in the Eucharist. During the last part of his life he understood that what he had concluded at the beginning about the Sermon on the Mount - that is, now that we are Christians, we live this ideal permanently - was mistaken. Only Christ himself truly and completely accomplishes the Sermon on the Mount. We always need to be washed by Christ, who washes our feet, and be renewed by him. We need permanent conversion. Until the end we need this humility that recognizes that we are sinners journeying along, until the Lord gives us his hand definitively and introduces us into eternal life. It was in this final attitude of humility, lived day after day, that Augustine died.
This attitude of profound humility before the only Lord Jesus led him also to experience an intellectual humility. Augustine, in fact, who is one of the great figures in the history of thought, in the last years of his life wanted to submit all his numerous works to a clear, critical examination. This was the origin of the Retractationum ("Revision"), which placed his truly great theological thought within the humble and holy faith that he simply refers to by the name Catholic, that is, of the Church. He wrote in this truly original book: "I understood that only One is truly perfect, and that the words of the Sermon on the Mount are completely realized in only One - in Jesus Christ himself. The whole Church, instead - all of us, including the Apostles -, must pray everyday: Forgive us our sins as we forgive those who sin against us" (De Sermone Domini in Monte, I, 19, 1-3).
Augustine converted to Christ who is truth and love, followed him throughout his life and became a model for every human being, for all of us in search of God. This is why I wanted to ideally conclude my Pilgrimage to Pavia by consigning to the Church and to the world, before the tomb of this great lover of God, my first Encyclical entitled Deus Caritas Est. I owe much, in fact, especially in the first part, to Augustine's thought. Even today, as in his time, humanity needs to know and above all to live this fundamental reality: God is love, and the encounter with him is the only response to the restlessness of the human heart; a heart inhabited by hope, still perhaps obscure and unconscious in many of our contemporaries but which already today opens us Christians to the future, so much so that St Paul wrote that "in this hope we were saved" (Rom 8: 24). I wished to dedicate my second Encyclical to hope, Spe Salvi, and it is also largely indebted to Augustine and his encounter with God.” (Benedict XVI, February 27, 2008.)