New Wine and Old Wine I am curious about the connection Jesus makes between fasting and New Wine. Many people relate it to the idea of appropriateness. It just strikes me as an odd comparison.
To understand the link between fasting and the parables Jesus gave in answer in Mark 2:18-22 (ESV), we need to note that the Mosaic Law prescribed only one fast on the Day of Atonement (Leviticus 16:29, 31).  However, the legalistic Pharisees and the disciples of John the Baptist were following the traditions of men.

Now John’s disciples and the Pharisees were fasting. And people came and said to him, “Why do John’s disciples and the disciples of the Pharisees fast, but your disciples do not fast?”  And Jesus said to them, “Can the wedding guests fast while the bridegroom is with them? As long as they have the bridegroom with them, they cannot fast. The days will come when the bridegroom is taken away from them, and then they will fast in that day.  No one sews a piece of unshrunk cloth on an old garment. If he does, the patch tears away from it, the new from the old, and a worse tear is made.  And no one puts new wine into old wineskins. If he does, the wine will burst the skins—and the wine is destroyed, and so are the skins. But new wine is for fresh wineskins.” (Mark 2:18-22 ESV)

The ESV Study Bible makes these comments:

Jesus refers to himself as the bridegroom, who in the O.T. was the Lord (cf. Isa. 62:5; Hos. 2:19-20).  While Jesus is present with his disciples, they are to rejoice; when he is taken away from them, then they will fast.
Just as new, ushrunk cloth cannot coexist with an old garment, the kingdom of God cannot be regarded merely as a patch over the regulations of the Mosaic law and extra-biblical traditions.  New wine vs. old wineskins illustrates the same truth – that Jesus brings a new era with new ways.

The reason it is inappropriate to put new wine into old wineskins is that the wine will burst the skins, destroying both the wine and the skins.
These two parables illustrate the fact that you can’t mix old religious rituals with new faith in Jesus. Jesus’ disciples were not fasting along with the Pharisees and John’s disciples because they were now under the new covenant of grace and faith in Christ.