'No-one sews a piece of unshrunk cloth on an old garment. If he does, the patch tears away for 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 2:21-22)
Jesus is teaching here about the new life of the kingdom of God. We quickly understand that the new wine is the new life we have in Christ, 'this cup is the new covenant in my blood.' Try to keep new wine - which is full of life and fizz - in an inflexible, brittle, leather skin and the skin breaks and the wine is lost. (This is why today lively, young wines, such as Beaujolais Nouveau, are bottled in thicker glass than those that have matured longer in the cask.)
The parallel illustration of the new patch on the old garment is even more ridiculous. Imagine you have an old jacket, tattered, dirty, worn through at the elbows, and someone gives you a brand new jacket of the best quality. Which fool would cut pieces from the new to patch up the old?
Yet this is exactly what Jesus is warning us against: trying to use the new life we have in Christ to patch up the old life we had in Adam. Ridiculous isn't it? And what's more, not only does it not work, it actually makes our lives worse: the effect of the new is to expose even more the failings of the old, and we're left more miserable than when we began. If you're a miserable Christian, this could well be the reason!
The new life we have in Christ can only be worn whole. It must be embraced completely. Salvation isn't material given us to patch up an old life - it's a complete new suit of clothes designed to be worn at all times and for the rest of eternity.
The Christian life doesn't work at all unless Jesus is continually at the centre. In my experience, Jesus at the edge is the most uncomfortable & dissatisfying life imaginable. The new life in Christ is a radical transfer for the domain of darkness to the Kingdom of the Beloved Son. Don't try to patch the old - throw it out, and put on the new and be true to who you really are:
'Do not lie to one another, seeing that you have put off the old self with its practices and have put on the new self, which is being renewed in knowledge after the image of its creator' (Colossians 3:9-10).