The children of the Bridegroom also cannot fast, i. e. refuse nourishment to the soul, but live on every word which proceedeth out of the mouth of God.
(Orat. de Deit. Filii et SS.) For wine newly drawn forth, evaporates on account of the natural heat in the liquor, throwing off from itself the scum by natural action. Such wine is the new covenant, which the old skins because of their unbelief contain not, and are therefore burst by the excellence of the doctrine, and cause the grace of the Spirit to flow in vain; because into an evil soul wisdom will not enter. (Sap. 1:4.)
At the same time also is shown the difference between those who are zealous for the law and those who are for grace, that they who follow the law shall suffer eternal hunger of soul, while they who have received the word into the inmost soul, refreshed with abundance of heavenly meat and drink, can neither hunger nor thirst. And so they who fasted in soul murmured.
Or, That fast is not given up whereby the flesh is mortified, and the desires of the body chastened. (For this fast commends us to God.) But we cannot fast who have Christ, and banquet on the flesh and blood of Christ.
But when are those days, in which Christ shall be taken away from us, since He has said, I will be with you alway, even unto the end of the world? But no one can take Christ away from you, unless you take yourself away from Him.
Lastly, it is spoken of the fast of the soul, as the context shows, for it follows, But he said, No man putteth a piece of a new garment upon an old. He calleth fasting an old garment, which the Apostle thought should be taken off, saying, Put off the old man with his deeds. (Col. 3:9.) In the same manner we have a series of precepts not to mix up the actions of the old and new man.
The weakness of man's condition is exposed when our bodies arc compared to the skins of dead animals.
(ubi sup.) But the Apostles are compared to old skins, who are more easily burst with new wine, i. e. with spiritual precepts, than contain them. Hence it follows, Else the new wine will burst the skins, and the wine will be spilled. But they were new skins at that time, when after the ascension of the Lord they received the Holy Spirit, when from desire of His consolation they were renewed by prayer and hope. Hence it follows, But the new wine must be put into new bottles, and both are preserved.
Those who live according to the law cannot receive the institutions of Christ. These institutions cannot be admitted into the hearts of such as have not as yet received the renewing by the Holy Spirit. The Lord shows this by saying that a tattered patch cannot be put upon a new garment, nor can old skins hold new wine. The first covenant has grown old, nor was it free from fault. Those, therefore, who adhere to it and keep at heart the antiquated commandment have no share in the new order of things in Christ. In him all things are become new, but their mind being decayed, they have no harmony or point of mutual agreement with the ministers of the new covenant.
For as long as the Bridegroom is with us we both rejoice, and can neither fast nor mourn. But when He has gone away through our sins, then a fast must be declared and mourning be enjoined.
Inasmuch as wine refreshes us within, but garments cover us without, the garments are the good works which we do abroad, by which we shine before men; wine, the fervour of faith, hope, and charity. Or, The old skins are the Scribes and Pharisees, the new piece and the new wine the precepts of the Gospel.
But to every soul which is not yet renewed, but goes on still in the old way of wickedness, the sacraments of new mysteries ought not to be given. They also who wish to mix the precepts of the Law with the Gospel, as the Galatians did, put new wine into old bottles. It follows, No man also having drank old wine straightway desireth new, for he saith, the old is better. For the Jews, imbued with the taste of their old life, despised the precepts of the new grace, and being defiled with the traditions of their ancestors, were not able to perceive the sweetness of spiritual words.
[AD 379] Basil of Caesarea on Luke 5:33-39