Luke 5:37

(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.)

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.

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.

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.