Mark 2:21-22

2:21 No one sews a patch of unshrunk cloth on an old garment; otherwise, the patch pulls away from it, the new from the old, and the tear becomes worse. 2:22 And no one pours new wine into old wineskins; ¹  otherwise, the wine will burst the skins, and both the wine and the skins will be destroyed. Instead new wine is poured into new wineskins.” ² 

¹ sn Wineskins were bags made of skin or leather, used for storing wine in NT times. As the new wine fermented and expanded, it would stretch the new wineskins. Putting new (unfermented) wine in old wineskins, which had already been stretched, would result in the bursting of the wineskins.

² sn The meaning of the saying new wine is poured into new skins is that the presence and teaching of Jesus was something new and signaled the passing of the old. It could not be confined within the old religion of Judaism, but involved the inauguration and consummation of the kingdom of God.