Let not the Christian say: “I am free; I have been called unto liberty. I was a slave, but have been redeemed, and by my very redemption have been made free so I shall do what I please; no one may restrict my will, if I am free.” But if you commit sin with such a will, you are the servant of sin. Do not then abuse your liberty for freedom in sinning, but use it for the purpose of not sinning. For only if your will is pious will it be free. You will be free if you are a servant still—free from sin, the servant of righteousness.
SAINT AUGUSTINE Tractates on the Gospel of John
