Mark 2:22

And no man putteth new wine into old wine-skins: else the wine will burst the skins, and the wine perisheth, and the skins: but they put new wine into fresh wine-skins.

Skins of animals were used in those times for containing liquids; and, in the case of wine, if new, the process of fermentation increased the volume which was compensated for by the elasticity of the new skins. However, if new wine was put into old skins (hardened and no longer elastic), the fermentation process would burst them, resulting in the loss of both the wine and the wineskins.

The application of this has been understood to mean that Jesus' new teaching could not be put into John's disciples; but it seems preferable to make the forms, ceremonies, and ordinances of Judaism to be the old wineskins; and Jesus' new teachings could not be subordinated to and synchronized with such things as Jewish fasts. To understand this to mean that Jesus would not put his new teaching into John's disciples violates the fact that some of John's disciples became apostles of Christ (John 1:35). However, the majority seem not to have done so; and the reluctance of many of John's disciples to follow Jesus would appear to be the primary meaning of the third phase of this triple reply. "No man having drunk old wine desireth new; for he saith, The old is good" (Luke 5:89). Thus, if certain exceptions are noted, it may still be appropriate to understand the old wineskins as John's disciples.