Augustine, City of God, Book 10, Chapter 6
Thus the true sacrifice is every work which is carried out so that we may cling to God by a holy bond (societas) i.e. it is directed toward that good end (end of the good One) in which we can be truly blessed. From this mercy itself which comes to man is only a sacrifice if it is done from God’s sake. For even if it is done or offered by a man, yet a sacrifice is a divine thing (res divina) so that even the old Latins called it by this name. So, a man himself who is consecrated in the name of God and devoted to God is a sacrifice to the extent that he dies to the world and lives to God. For this too pertains to mercy when each one does for himself. Further it is written, “Have mercy on your soul by pleasing God.”
Our body too is a sacrifice when we discipline it with temperance. We do this, as we should, for God’s sake. The result is that we do not present our members to sin as weapons of iniquity but to God as weapons of justice. The apostle exhorts us about this by saying, “I appeal to you, brothers, through the mercy of God to present your bodies as a living sacrifice, holy, pleasing to God, as your rational service.
Augustinus, De Civitate Dei, Lib. X, Cap. 6
Proinde verum sacrificium est omne opus, quo agitur, ut sancta societate inhaereamus Deo, relatum scilicet ad illum finem boni, quo veraciter beati esse possimus. Unde et ipsa misericordia, qua homini subvenitur, si non propter Deum fit, non est sacrificium. Etsi enim ab homine fit vel offertur, tamen sacrificium res divina est, ita ut hoc quoque vocabulo id Latini veteres appellaverint. Unde ipse homo Dei nomine consecratus et Deo votus, in quantum mundo moritur ut Deo vivat, sacrificium est. Nam et hoc ad misericordiam pertinet, quam quisque in se ipsum facit. Propterea scriptum est: Miserere animae tuae placens Deo.
Corpus etiam nostrum cum temperantia castigamus, si hoc, quem ad modum debemus, propter Deum facimus, ut non exhibeamus membra nostra arma iniquitatis peccato, sed arma iustitiae Deo, sacrificium est. Ad quod exhortans Apostolus ait: Obsecro itaque vos, fratres, per miserationem Dei, ut exhibeatis corpora vestra hostiam vivam, sanctam, Deo placentem, rationabile obsequium vestrum.