A lot of people know what Jesus said, but they don't understand what it means to us today in reference to the new patch on an old cloak and new wine in an old wineskin. In Mark 2.21-22 Jesus said, "No one sews a piece of unshrunk cloth on an old cloak; otherwise, the patch pulls away from it, the new from the old, and a worse tear is made. And no one puts new wine into old wineskins; otherwise, the wine will burst the skins, and the wine is lost, and so are the skins; but one puts new wine into fresh wineskins."
It is common knowledge that if you sew a new patch that hasn't been preshrunk onto an old worn pair of jeans, the first time you wash them the new patch will shrink and the jeans will be a mess. Likewise in ancient days, before wine bottles were invented, wine was stored in wineskins made of animal hide or gut. If new wine was poured into a wineskin that had been previously used, the fermentation process would burst the wineskin. This would not have been good for the wineskin or to the wine. They both would have been ruined.
Besides, to put new wine into an old wineskin would be asking for big trouble. The old wineskin has assumed a definite shape and is no longer pliable. It is fixed and somewhat brittle. The essence of this is that you can't put new ideas into old mindsets. You can't get new results with old behaviors.
Too often people start a new relationship; however, they bring along old ideas into the new relationship and before long they have ruined the relationship.
Putting new wine in old wineskin was just an analogy that Jesus was teaching that some new things just don't go along with some old things. Old stuff wears out and becomes unsuitable for use with new materials. When you put fresh wine in an old wineskin, the new wine interacts more strongly than an aged wine would and the bag will eventually burst.
The point of the analogy is that new ideas and new ways of behaving are incompatible with old mindsets. In other words, people can't bring along old habits and beliefs if they want a changed life. Otherwise, it might do more harm than good.
Too often we have heard people say, "I have always done it this way." That's the point. You can't do things the old way and expect new results. Don't bring old bad habits into a new relationship. Don't bring the same things on a new job that got you fired from your old job. If you want things to be better in your life, don't put new wine in old wineskin.