When Augustine visited Hippo from Thagaste in the year 389, it resulted in the unintended outcome of propelling him to priesthood. While in his lay community at Thagaste in the year 389, Augustine went to Hippo to see a friend who was interested in setting up a similar community there. Thirty-five years later, he recounted in Sermon 355 how greatly this visit changed his life. In Hippo "I was grabbed," he explained. Augustine was not exaggerating; he was pressed into becoming a priest.

It had not been his intention to become a priest. Indeed, he had been avoiding it because he wished to lead a private life in his community of lay people at Thagaste. When he was at Mass in Hippo the aged bishop, Valerius, saw Augustine in the congregation. In his sermon Valerius was describing the urgent need of the local Catholic minority, which was surrounded by sects such as the Donatists. And then, without warning, Valerius added, "This congregation is in need of more priests, and I believe that the calling of Augustine to the altar would be to the honour of God." Willing hands propelled Augustine forward, and the bishop and congregation prevailed upon Augustine to say yes. The only condition that Augustine sought and was granted was that he be allowed time for study and preparation beforehand. Although not wanting to give up his life of study and prayer as a lay person in a community, Augustine nevertheless agreed to the request of the people. In a sermon much later in life, Augustine said to his people, 

"A slave may not contradict his Lord. I came to this city to see a friend, whom I thought I might gain for God, that he might live with us in our community at Thagaste. I felt secure, for the place already had a bishop. I was grabbed. I was made a priest . . . and from there, I became your bishop." In his book, City of God, he said "No one should be so given to contemplation that in this condition he gives no thought to the needs of his neighbour; nor so given to activity that he allow no time for the contemplation of God... The love of truth seeks out holy leisure, but the compelling force of love takes on necessary activity. But if no one imposes this burden, time should be passed in searching out and looking into truth. If, however, the burden is imposed, it ought to be borne because of the compelling force of love. However, not even in this case should the delight for learning be entirely abandoned, lest that delight be lost and the burden crush him." [City of God, 19, 19]

Before becoming a bishop. Augustine had five years of priesthood (391-396). He began this ministry not later than the Easter of 391, when he preached to the candidates for baptism in Hippo. Valerius had insisted that he preach, in spite of the custom in Africa of reserving that ministry to bishops. These years as a priest were quite a formative time for him. As a priest, Augustine devoted himself to the study of Scripture in a different way than before, and even successfully sought otium ("study leave") from Bishop Valerius of Hippo in order to do so. He prepared himself for the years ahead. There would be struggles with heretics and a huge amount of writing that he would undertake. During this period he wrote the first of his treatises against the Manichees. The dialogues that Augustine wrote at Cassiciacum the year following his conversion and preceding his baptism showed few substantial signs of a theological understanding that was decisively or distinctively Christian.

By the time of his ordination to the presbyterate, however,the basic lines of a comprehensive and orthodox theology within him were firmly laid out. Augustine neglected to write about what had happened in his thought between 385 and 391. He had other questions, more interesting to him, with which to wrestle. While he was a priest Augustine combated heresy, especially Manichæism, which in earlier years he himself had followed. Partly because of this past experience with it, his success against Manichaeism was notable. Fortunatus, one of their scholars and a Manichean priest at Hippo, whom Augustine debated in a public conference in 392, was so humiliated by his defeat that he fled from Hippo. Other details of this period are that Augustine appealed to Aurelius, Bishop of Carthage, to suppress the custom of holding banquets and entertainments in the churches. By the year 395 Augustine had succeeded, through his courageous words, in abolishing this custom in Hippo.

As well, his treatise De fide et symboli ("About Faith and symbols") was prepared to be read before the bishops of the region assembled at the Council held at Hippo on 8 October 393. After that he travelled to Carthage, which was to become the most frequent destination of all of his subsequent journeys. Augustine remained there for a while, perhaps in connection with the synod held there in 394. In summary, the time which Augustine spent in the presbyterate (391-396) were the last years of his formative period. His earliest written works from the year 396 onwards reveal the fully developed Christian thinker of whose special teaching we think when we speak of Augustinianism. This demonstrates that his five years of priesthood had been, therefore, an important time of intellectual growth for him. As a very new priest, Augustine placed before Valerius, his bishop, a respectful demand. Augustine thought that Valerius had almost no choice when responding; the only realistic answer to the letter from Augustine was that his request be granted. Valerius knew that Augustine had been "grabbed" for priesthood - as Augustine himself had described it - by the Hippo congregation, even possibly with the connivance of Valerius himself; this unexpected and muscular persuasion had caught Augustine not only by surprise but also unprepared.

Augustine had suddenly been transferred from his dedicated lay membership in the church to the sacrament and ministry of priesthood. He did this without moving gradually through any of the intermediate clerical grades such as lector, subdeacon, or deacon.; he may have been concerned that others would not have approved his rapid promotion through these grades of Holy Orders. Even if that were not so, Augustine himself in any case was clearly aware of the inadequacy of his hurried preparation for his ministry. This would have been especially true of the role of preaching into which Bishop Valerius promoted Augustine while he was still a priest and not yet a bishop. For a priest to preach was quite exceptional in the church in North Africa until Augustine broke that pattern. From what is known of his style of preaching, Augustine certainly sought further time for the otium ("holy leisure") of absorbing the Scriptures.

Another motivation open to Augustine was that as a lay person he had himself been a vocal critic of clergy who were inadequately trained for duty. Now he suddenly he felt he was in that situation himself. He now experienced the real dangers and actual demands of priestly ministry, and as a result proposed a two-fold remedy to his bishop. The first part was already happening: he had learned virtue by recognising his weakness (a task that his Confessions would show future ages soon after he became a bishop). The second part of his remedy could only be addressed by an intense study of the Scriptures, which in his letter to Valerius he called "the medication of God." He wrote to Valerius, "I ought to carefully consider God's medication in the Scriptures. I can do this by prayer and reading, in order that strength sufficient for such dangerous obligations (as priesthood) may be granted to me." (Letter 21,3) Studying the Gospel, praying them, and translating them into deeds: this was the preparation that Augustine saw himself as needing. He thus respectfully asked Valerius to grant him a period of time free of pastoral duty, a request that apparently was granted.

Resource

For further details, go to "Clericatus sarcina (ep.126.3): Augustine and the Care of the Clergy" by the late Thomas F. Martin, O.S.A., Ph.D., who was a director of Augustinian studies at Villanova University, Pennsylvania, in the United States of America.

Link

The ordination of Augustine. - A scholarly coverage in The Internet Encyclopedia of Philosophy. Scroll down to the appropriate section.
http://www.iep.utm.edu/augustin