Luke 5:36
And he spake also a parable unto them; No man putteth a piece of a new garment upon an old; if otherwise, then both the new maketh a rent, and the piece that was taken out of the new agreeth not with the old. And he spake also a parable unto them; No man putteth a piece of a new garment upon an old; if otherwise, then both the new maketh a rent, and the piece that was taken out of the new agreeth not with the old.
The parable also reaches back to John the Baptist, whose devotion could not be blended with Pharisaic tradition, superstition and pretense, and any attempt to unite the two would only make the breach between them clearer. Christ's teaching likewise could not be united with Pharisaism in its fixed forms and human rules, and rather than repairing the breach it made the separation between the old religion and the new truth distinct. His new principles cannot be sewn as a patch onto the false religion of the scribes and Pharisees, because the two do not harmonize and remodelling that old religion is out of the question. Trying to join them does not mend the rent but tears away and makes it worse.
The old garment is a manufactured religion of outward ceremony, exactions, traditions and forms trusted for salvation while the heart remains proud, selfish, covetous, oppressive and wicked. It is blind to God and without mercy, love and compassion for the poor. The new cloth is the truth, life, light and righteousness of heart that belong to true godliness. Form and ceremony can never take the place of righteousness, so to put the two together only makes the rent worse.
More generally, Jesus' teaching cannot be added as a patch to the old religious life, for His disciples must be made entirely new in character and live by new principles. Understanding truth and following Him require the new birth, giving up old religious theories, human customs and teachings that make human commandments into doctrine. His religion calls for whole-hearted obedience with self-denial and self-sacrifice, and sets a higher and holier standard than the teachings of the Pharisees.
True repentance discards the old pharisaical garment of self-righteousness altogether instead of trying to mend it with new cloth. Covering up and excusing the sin of the natural heart leaves the heart unchanged and still sending forth bitter waters, while genuine repentance changes the heart and brings reformation without excuse or defense of sinful actions. The one who with loathing of soul sees a defective character that has dishonored Christ and in contrition asks forgiveness no longer excuses and vindicates actions that brought reproach on the cause of God. Such a one is filled with thankfulness for not being blinded until too late for wrongs to be righted, and saves the soul unto eternal life.
The image of a new patch that does not fit the old garment and only makes the tear worse applies to trying to humble other people instead of humbling oneself. That course worsens the harm, and the Lord turns away from such work. Every heart must feel its own peril, humble its own heart, confess its own sins, and place itself where God can bless it.