Numbers 28:7

Since, therefore, we have in our hands the laws of the feasts, and the discourse is now about them, let us inquire more diligently what the order of the festivals is, so that from the very orders and the rite of the sacrifices we may be able to gather how each one, out of his own acts and holy conversations, may be able to prepare a festivity for God. The first, then, of God's festivals is that which is called "unceasing"; for the command is about those things which are to be offered unceasingly and without any interruption at all in the morning and evening sacrifices. Therefore, in commanding the rites of the festivals, He did not come first at once to the festival of the Passover, nor to that of the unleavened bread, nor to that of tabernacles and the others concerning which He gives command, but He set this one first, in which He commands the unceasing sacrifice to be offered — so that whoever wishes to be perfect and holy may recognize that a festivity is not to be kept to God sometimes and sometimes not, but the just man ought always and unceasingly to keep a feast day. For the sacrifice which is commanded to be offered unceasingly, both in the morning and in the evening, indicates this: that in the law and the prophets, which show the morning time, and in the evangelical teaching, which shows the evening, that is, the coming of the Savior at the evening of the world, one should persist with unceasing attention. Such festivals, then, the Lord calls His own: "And you shall observe my feast days." It is therefore the Lord's feast day, if we offer Him sacrifice unceasingly, if we pray without intermission, so that our prayer ascends like incense in His sight in the morning, and the lifting up of our hands becomes to Him the evening sacrifice. The first solemnity, then, is that of the unceasing sacrifice, which by the worshippers of the Gospel ought to be fulfilled in the manner we have expounded above. But since, as the prophetic word has fully taught, the feast days of sinners are turned into mourning and their songs into wailing, it is certain that he who sins and keeps days of sin cannot keep a feast day; and therefore on those days on which he sins he cannot offer the unceasing sacrifice to God. But he can offer it who unceasingly keeps justice and preserves himself from sin. But on whatever day he interrupts this and sins, it is certain that on that day he does not offer the unceasing sacrifice to God. I am afraid to say something which is given to be understood from the Apostolic discourses, lest perhaps I seem to sadden some. For if the prayer of the just man is offered like incense in the sight of God, and the lifting up of his hands is the evening sacrifice, but the Apostle says to those who are in marriages: "Defraud not one another, except perhaps by consent for a time, that you may have leisure for prayer, and return again to the same," it is certain that the unceasing sacrifice is hindered for those who serve the necessities of marriage. Hence it seems to me that it belongs to him alone to offer the unceasing sacrifice, who has devoted himself to unceasing and perpetual chastity. But there are also other feast days for those who perhaps cannot unceasingly immolate the sacrifices of chastity.