In the Old Testament, God constantly called Israel to repent, but Israel constantly fell into a cycle of infidelity. This brought hardships which Israel understood as God's punishment. They responded in repentance and returned to the Lord.
Even without falling into this cycle of infidelity, we realize that conversion is a growth process. Its first-moment may be an instantaneous one as in Paul's case.
As a faithful and fervent Jew, a Pharisee, Paul was already converted to the Lord. His Jewish faith was leading him to experience God more. Paul had to abandon much to become rich in Christ.
Even though Paul's conversion to Jesus was a sudden occurrence, it did have a background and a future. His experience, as we have noted, was his Jewish faith and fidelity. His life was a continual growth in Christ, an increase in holiness. Paul's sudden conversion was absolute and irreversible, but it was the beginning rather than the end of a journey. It was his first step on the pathway of Christian holiness. Thus in his letter to the Philippians reflecting upon his Christian life, he talks about it as a "race" a "striving forward."
Lord, help us to be faithful to the grace of our baptism and to grow in holiness in Christ Jesus Our Lord.