No one sews a piece of new, unshrunk cloth onto an old garment. otherwise the new patch will tear away completely from the old garment, and the tear will be worse.
This parable shows that the newness brought by Christ cannot simply be attached to old religious forms as if nothing will change. Adding a new patch to an old garment is an outward solution that in fact deepens the problem. In the same way, the Gospel did not come merely to add a few pious additions to people’s old, self-justifying and tradition-bound way of thinking. It brings inner renewal, a new heart, and a new relationship with God. If a person tries to fit the truth of Christ into an old self-centered or merely formal religious life without complete repentance, the result is even greater confusion.