St. Augustine shows us that religion abides in our heart because it is not just an idea but a person: Christ. The Old Testament was based on the law; pagan religions were based on state cult. For both, religion was a set of obligations. For St. Augustine, religion is lived through faith: a personal encounter with Christ that leads to adherence based in love.
Meaning of sacrifice. Before Christ, the individual person had no inherent value, it was an asset that could be disposed of. Christ reveals a new understanding of the person and sacrifice. He sacrificed Himself, but rose victorious, giving us new life. The Christian, like Christ, sacrifices himself to become a member of Christ's Body, but his "self" is not annihilated, it is raised to the fullness of its potential and lives forever. He suffers with Christ and shares in His glory. Through sacrifice the individual breaks the ties that keep him bound to sin and imperfection, he expands his capacity to love and bring new life to many.