Matthew 9:16 English Standard Version (ESV) No one puts a piece of unshrunk cloth on an old garment, for the patch tears away from the garment, and a worse tear is made.

Since Jesus first addresses their understanding of religious exercises, the second challenge is over their identity. Garments represent status, i.e. the priest desiring the best robes, to look good, to appear righteous where righteousness is seen as the whitest robes with not one spot of blood on them.

The old garment the old identity is in reference to becoming this new creation in Christ. This newness of life should take on a new appearance, one which shows a change in both character and worship. Since that old identity was closely associate with the OT law, what does this new identity look like?

For one thing it cannot be a patch of torn identity, one cannot keep the OT law and this new identity which is based on our being the bride and Jesus the bridegroom. Our identity is His identity, because we have become one flesh in betrothal.

Isaiah 1:5 English Standard Version (ESV) Why will you still be struck down? Why will you continue to rebel? The whole head is sick, and the whole heart faint.

The head needs to change to one that is not sick.

1 Corinthians 11:3a English Standard Version (ESV) But I want you to understand that the head of every man is Christ,

Ephesians 1:22 English Standard Version (ESV) And he put all things under his feet and gave him as head over all things to the church,

Colossians 2:10 English Standard Version (ESV) and you have been filled in him, who is the head of all rule and authority.

1 Corinthians 2:16b English Standard Version (ESV) But we have the mind of Christ.

We have the mind of Christ, He is our Lord, our bridegroom, in whom our identity is securely fixed.

Matthew 9:15 English Standard Version (ESV) And Jesus said to them, “Can the wedding guests mourn as long as the bridegroom is with them? The days will come when the bridegroom is taken away from them, and then they will fast.

Beyond the general concept of Jesus being the bridegroom here, there is a challenge to the practices being observed by those who worship God in fasting. Since these new disciples need not fast as long as Jesus (the Messiah) is present with them, why do those who worship God fast? What is there understanding of fasting? Jesus is challenging their understanding and their practice.

“Many customs, purely secular in their origin, have gradually obtained a religious significance, just as purely religious customs have been dissociated from religion. It is also possible and, in the light of some usages, probable, that different motives operated in the association of fasting, as of some other customs, with religion. Scholars have been too ready to assume that the original significance of fasting was the same in all countries and among all nations. Robertson Smith in his Religion of the Semites advanced and defended theory that fasting was merely a mode of preparation for the tribal meal in which sacrifice originated, and came to be considered at a later stage as part of the sacrificial act. This hypothesis apparently accounts for the otherwise strange fact that both fasting and feasting are religious acts, but it does not give a satisfactory explanation of the constant association of fasting with the “wearing of sackcloth,” the “putting of ashes on the head,” and other similar customs. It is obvious that very different motives operated in the institution of fasting and of feasting religious observances.” Ref. quoted from International Standard bible Encyclopedia

Leviticus 16:29 offers a statute in which Israel was told to afflict themselves before the atonement sacrifice was made. That affliction was defined as humbling oneself and over time has been used by religious leaders to call for a fast, to deny the flesh. Note the difference between the statute and the practice.