For those who just can't bear to wade through the clunky NPNF translation, here are our own favorite bits, handily excerpted. Mind you, we can't do justice to Augustine's whole case, but we can provide a taste to sharpen the appetite.
1. Jesus is the Liberating Truth:
The truth is unchangeable. The truth is bread, which refreshes our minds and fails not; changes the eater, and is not itself changed into the eater. The truth itself is the Word of God, God with God, the only-begotten Son.
This Truth was for our sake clothed with flesh, that He might be born of the Virgin Mary, and the prophecy fulfilled, “Truth has sprung from the earth.” (Ps. 85) This Truth then, when speaking to the Jews, lay hid in the flesh. But He lay hid not in order to be denied, but to be deferred [in His manifestation]; to be deferred, in order to suffer in the flesh; and to suffer in the flesh, in order that flesh might be redeemed from sin.
And so our Lord Jesus Christ, standing full in sight as regards the infirmity of flesh, but hid as regards the majesty of Godhead, said to those who had believed on Him, when He so spake, “If ye continue in my word, ye shall be my disciples indeed.” For he that endureth to the end shall be saved. (Matthew 10:22) “And ye shall know the truth,” which now is hid from you, and speaks to you. “And the truth shall free you.”After this follows a brief discourse on Latin usage compared with Greek, which bored even us.
2. Slavery to Sin is Worse than Ordinary Slavery:
Men [i.e., slaves] frequently, when they suffer under wicked masters, demand to get themselves sold, not seeking to be without a master, but at all events to change him. What can the servant of sin do? To whom can he make his demand? To whom apply for redress? Of whom require himself to be sold?
And then at times a man’s slave, worn out by the commands of an unfeeling master, finds rest in flight. Whither can the servant of sin flee? Himself he carries with him wherever he flees. An evil conscience flees not from itself; it has no place to go to; it follows itself.
Yea, he cannot withdraw from himself, for the sin he commits is within. He has committed sin to obtain some bodily pleasure. The pleasure passes away; the sin remains. What delighted is gone; the sting has remained behind.
Evil bondage! Sometimes men flee to the Church, and we generally permit them, uninstructed as they are — men, wishing to be rid of their master, who are unwilling to be rid of their sins. But sometimes also those subjected to an unlawful and wicked yoke flee for refuge to the Church; for, though free-born men, they are retained in bondage: and an appeal is made to the bishop. And unless he care to put forth every effort to save free-birth from oppression, he is accounted unmerciful.
Let us all flee to Christ, and appeal against sin to God as our deliverer. Let us seek to get ourselves sold, that we may be redeemed by His blood. For the Lord says, “Ye were sold for nought, and ye shall be redeemed without money.” (Isaiah 52:3) Without price, that is, of your own; because of mine. So saith the Lord; for He Himself has paid the price, not in money, but His own blood.It bears repeating that Greco-Roman slavery was a rather different system than the one familiar to Americans, and that this example should therefore be cited only with great care.
3. Freedom for Love:
Since, then, every one that committeth sin is the servant of sin, listen to what is our hope of liberty.
“And the servant,” He says, “abideth not in the house for ever.” The church is the house, the servant is the sinner. Many sinners enter the church. Accordingly He has not said, “The servant” is not in the house, but “abideth not in the house for ever.” If, then, there shall be no servant there, who will be there? [....]
He has greatly alarmed us, my brethren, by saying, “The servant abideth not in the house for ever.” But He further adds, “But the Son abideth ever.” Will Christ, then, be alone in His house? Will no people remain at His side? Whose head will He be, if there shall be no body? Or is the Son all this, both the head and the body? For it is not without cause that He has inspired both terror and hope: terror, in order that we should not love sin; and hope, that we should not be distrustful of the remission of sin. [....]
Our hope is this, brethren, to be made free by the free One; and that, in setting us free, He may make us His servants. For we were the servants of lust; but being set free, we are made the servants of love.
This also the apostle says: “For, brethren, ye have been called unto liberty; only use not liberty for an occasion to the flesh, but by love serve one another.” (Galatians 5:13) Let not then 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, I shall do what I please: no one may balk me of my will, if I am free. But if thou committest sin with such a will, thou art the servant of sin. Do not then abuse your liberty for freedom in sinning, but use it for the purpose of sinning not. For only if thy will is pious, will it be free.4. Liberty is Eschatological:
What then is that full and perfect liberty in the Lord Jesus ... and when shall it be a full and perfect liberty?
When enmities are no more; when “death, the last enemy, shall be destroyed.” “For this corruptible must put on incorruption, and this mortal must put on immortality. —And when this mortal shall have put on immortality, then shall be brought to pass the saying that is written, Death is swallowed up in victory. O death, where is thy struggle?”
What is this, “O death, where is thy struggle”? “The flesh lusteth against the spirit, and the spirit against the flesh,” (1 Corinthians 15) but only when the flesh of sin was in vigor. “O death, where is [now] thy struggle?” Now shall we live, no more shall we die, in Him who died for us and rose again: “that they,” he says, “who live, should no longer live unto themselves, but unto Him who died for them and rose again.” (2 Corinthians 5:15)There's also a nice bit about the Prodigal Son, in which the Church is portrayed as the innkeeper. Not sure that does us much good right now, but it's worth coming back to.
As usual, Augustine's concerns are not precisely our own; but they are close enough that many Lutherans will recognize them instinctively. In particular, most Christians will recognize the perennial concern that liberty in Christ not become license to sin, but rather a new power to love.