Psalms 54:6

Listen to the prophet's voice: "I will freely sacrifice to you, O Lord." Learn how different an imposed servitude is from a voluntary one. A person who finds his own negligence accusing himself of suffering self-imposed servitude can never pass a day without regret. A person who obeys his Lord because of some solemn promise and thus reluctantly gains grace has stored up an injury for himself, since the prophet says, "Cursed is he who does the works of the Lord negligently." If each one of you reflects on the wonderful gift of the acquired liberty that our Christ has granted to his faithful people through the regeneration of the life-giving bath [baptism] and through the pouring out of the Holy Spirit, he understands that God should not be served halfheartedly. Even though we daily give God whatever honor or gift we can, we never pay him all we owe.

For among them (the Egyptians) these offices, which we are taught to render to the Lord at separate hours and at intervals of time with a reminder from the convener, are celebrated freely and continuously throughout the whole day in conjunction with their work. For manual labor is continuously practiced by them in their cells in such a way that meditation on the Psalms and the rest of the Scriptures is always before them. To this at every moment they mingle short petitions and prayers, spending the whole day in those offices which we celebrate at fixed times. Thus, except for vespers and nocturns, there are no public services among them in the day except on Saturday and Sunday, when they meet together at the third hour for the purpose of Holy Communion. For what is continuously offered is greater than what is rendered at intervals of time. And a free gift is more acceptable than the duties which are performed by the compulsion of a rule. For such as this, David rejoices somewhat exultingly when he says, "Freely will I sacrifice to you;" and, "Let the free will offerings of my mouth be pleasing to you, O Lord."

For next there follows: I will sacrifice unto You freely. The sacrifices of the Law, which consisted of whole burnt-offerings and oblations of goats and of bulls, did not involve an expression of free will, because the sentence of a curse was pronounced on all who broke the Law. Whoever failed to sacrifice laid himself open to the curse. And it was always necessary to go through the whole sacrificial action because the addition of a curse to the commandment forbad any trifling with the obligation of offering. It was from this curse that our Lord Jesus Christ redeemed us, when, as the Apostle says: Christ redeemed us from the curse of the law, being made curse for us, for it is written: cursed is every one that hangs on a tree. Galatians 3:13 Thus He offered Himself to the death of the accursed that He might break the curse of the Law, offering Himself voluntarily a victim to God the Father, in order that by means of a voluntary victim the curse which attended the discontinuance of the regular victim might be removed. Now of this sacrifice mention is made in another passage of the Psalms: Sacrifice and offering you would not, but a body have you prepared for Me ; that is, by offering to God the Father, Who refused the legal sacrifices, the acceptable offering of the body which He received. Of which offering the holy Apostle thus speaks: For this He did once for all when He offered Himself up Hebrews 7:27, securing complete salvation for the human race by the offering of this holy, perfect victim.