A few of St. Augustine's sermons on Lent have come down to us. This is a translation published in 1959 - you want sermons 205-211, that start on p. 185. I am not sure of the dating or specific context - they seem to have been preached in different years, since the themes carry over from sermon to sermon - such as the repeated reminder that if you abstain from some food or drink, it then makes no sense to replace what you have sacrifice with something that either is more costly or affords you as much or greater pleasure.
I appreciated this, from Sermon 207.
By the help of the merciful Lord our God, the temptations of the world, the snares of the Devil, the suffering of the world, the enticement of the flesh, the surging waves of troubled times, and all corporal and spiritual adversities are to be overcome by almsgiving, fasting, and prayer.
These practices ought to glow throughout the entire life of a Christian, but especially as the Paschal solemnity approaches which stirs up our minds by its yearly return, renewing in them the salutary memory that our Lord, the only-begotten Son of God, showed mercy to us and fasted and prayed for us. As a matter of fact, eleemosyna in Greek signifies mercy in Latin. Moreover, what mercy could be greater, so far as we poor wretches are concerned, than that which drew the Creator of the heavens down from heaven, clothed the Maker of the earth with earthly vesture, made Him, who in eternity remains equal to His Father, equal to us in mortality, and imposed on the Lord of the universe the form of a servant, so that He, our Bread, might hunger; that He, our Fulfillment, might thirst; that He, our Strength, might be weakened; that He, our Health, might be injured; that He, our Life, might die? And all this [He did] to satisfy our hunger, to moisten our dryness, to soothe our infirmity, to wipe out our iniquity, to enkindle our charity. What greater mercy could there be than that the Creator be created, the Ruler be served, the Redeemer be sold, the Exalted be humbled and the Reviver be killed?