"Be careful to observe all that I command you. Do not add to it, nor subtract from it" (Deut. 13:1).
It is obvious that it is wrong to stop observing one of the Torah's laws. But what is so terrible about adding a new one?
The Neighbor Who Liked to Borrow
Reuben once lent a plate to his neighbor Simon. A short while later, Simon returned the plate - but also brought along a small saucer.
"What is this saucer?" asked Reuben.
"Oh, the plate gave birth while it was at my house."
Weird, Simon thought to himself; but the little saucer looked to be quite useful.
A few weeks later, Simon came to borrow a pitcher. This time too, Simon returned the pitcher with a miniature pitcher, offering the same peculiar explanation of the big pitcher giving birth.
After a few months, Simon asked to borrow a set of silver candlesticks for a family occasion. Reuben was more than happy to oblige. But this time, Simon failed to return the article. Finally Reuben approached his neighbor.
"Simon, what happened to those candlesticks that you borrowed from me?"
"Oh, I'm very sorry," replied Simon, "The candlesticks died."
"What nonsense!" Reuben shouted. "Candlesticks don't die!"
Simon was not flustered, "When I told you that your plate and pitcher gave birth, you accepted this without question. If plates and pitchers can reproduce, then candlesticks can die!"
This parable explains the problem of inventing new mitzvot. If we allow ourselves to add our own laws, we will come to forget that the Torah and its laws are from God. And then we will soon find ourselves no longer observing those laws which seem to us too difficult or inconvenient.
(Adapted from Mishlei Yaakov, p. 394)