III. The Impossibility of Mixing the New with the Old (vv. 21-22)
a. The illustration of the unshrunk cloth
At this point you may be thing that it really isn’t all that big of a deal that these guys kept fasting according to their traditions, especially the disciples of John who disagreed with the Pharisees on virtually every other issue. However, in vv. 21-22 Jesus provides us with two illustrations to prove that it is impossible to mix the old with the new. You can either accept the new message of Jesus completely, or you will reject it completely. There is no middle ground. It is impossible to mix the two, in fact it is disastrous to even try and mix the two.
Jesus’ first illustration is found in v. 21 where He says, “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.” If you don’t know a lot about sowing then this really doesn’t make much sense. But when you understand what Jesus is saying it really is a brilliant illustration. The unshrunk clothe is a brand new piece of fabric that is intended to fix a hole in a piece of clothing. The problem is that the patch is unshrunk and the piece of clothing has already been shrunk. This means that when the piece of clothing is washed the new patch will shrink it will tear away from the piece of clothing. The result is a tear that is even worse than the original tear was. Thus, the patch was meant to fix the problem but instead it caused an even bigger problem.
The point of this illustration, as John MacArthur explains it, is that “Jesus’ new and internal gospel of forgiveness and cleansing cannot be attached to the old and external traditions of self-righteousness and ritual.” We cannot simply take the teaching of Jesus and attach it to the same old works based religion.
b. The illustration of the new wineskin
Additionally, the new teaching of Jesus cannot be contained in the old teaching of works based salvation. In v. 22 Jesus says, “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.” This illustration is also a bit confusing for us who do not store our wine in animal skin, but it is a powerful illustration when properly understood. In the first century wine would be stored leather pouches. When the wine was first made it would be stored in these leather pouches as it fermented. During the fermentation process the wine would actually expand. Because of this it was important to use new leather for the wine patches. If you used old leather, that had already been stretched, the expanding wine would cause the pouch to burst. The result would be the destruction of the wine and the wineskins.
In this illustration the wine represents the new teaching of Jesus and the old wineskin represents the man centered religion that was epitomized the by traditions of the elders and the perversions of the Old Testament. The gospel of Jesus was so different from the old man centered religion that the two could not coexist. This remains true today. The gospel of grace alone, by faith alone, through Christ alone, simply does not mix with a works based salvations. Whenever people try to mix these two the results are disastrous. No better example of this can be found than Roman Catholic Church. Through their attempts to mix works based religion with the teaching of Jesus the RCC perverts the message of Jesus, encourages people to trust in their own works, forsakes the teaching of all of Scripture, and it give people false hope for their own salvation.
As we look back on this passage it is clear that we must resist the temptation to hold onto the “old way” of works based salvation, and accept the “new way” of Jesus. It is impossible for us to mix the two, and even if we tried there would be disastrous results. With this in mind let me exhort you in several ways from the God’s word. If you have never accepted this new message of Jesus then you must do so. As Jesus said in Mark 1:15, “The time is fulfilled, and the kingdom of God is at hand; repent and believe in the gospel.” If you have accepted this new message of Jesus then continue to live in accordance with this new way. Do not fall back into the trap of the trusting in your own works. The apostle Paul dealt with Christians having this very problem in Galatians 3:3 where he said, “Are you so foolish? Having begun by the Spirit, are you now being perfected by the flesh?”
 John MacArthur, The MacArthur Commentary Series: Matthew (Chicago: Moody Press, ????), 70.