The Christian life, for Augustine, is a lifelong process of the recovery of freedom and of healing and transformation of the will that is initiated by grace, sustained by grace, and brought to completion by grace. Against the Manichaeans, he had argued that human beings are responsible for their actions and have free will. Against the Pelagians, he argues that grace is necessary if that free will is ever to become fully free. (When the Church Was Young: Voices of the Early Fathers by Marcellino D’Ambrosio)
What right has the Catholic Church to arrogate to herself powers given by Christ, rather than any other body of believers?
None whatever. No body of believers has any right to arrogate to itself any powers at all in this matter, just as no ordinary citizen has the right to enter a court and declare himself to be judge. Yet a lawfully appointed judge has the right to act in virtue of his commission. The Catholic Church takes nothing upon herself, but she does endeavor to fulfill the commission given her by Christ. Historically she alone can possibly inherit the jurisdiction given by Christ to the Apostles, and handed down through the ages. All other churches exist because men arrogated to themselves the right to coin new doctrines and set up churches of their own. (Radio Replies – by Charles M. Carty, Leslie Rumble)