Everyone knows about Moses hitting the rock. It was, as they say, an expensive mistake. It cost him his visa into the Land of Israel.

What is not readily understood is why hitting the rock was considered such a terrible sin. After all, when the Israelites first entered the desert and were in need of water, G-d Himself told Moses to hit the rock  Now, forty years into their walk in the wilderness, Miriam dies and the rock dries up. Water is again on the agenda. Only this time - hitting is not in order, only speaking is. Why?

The Midrash explains that the difference is the time lapse. Just because something worked once, doesn't mean it will work again!  You have to adapt to changing circumstances - and it takes great wisdom to know if, when and how.

I'm not only talking about adapting to technology or changed outer circumstances. The people closest to us are also in a state of flux - and it's a challenge to adapt to the ever-changing nature of the relationship. Let me give an example.

I know it's not the contemporary view, but Maimonides gives us pretty clear guidelines for educating children. When a child is young, says Maimonides, you need to treat him one way, when she's older, another. To encourage a young child to study Maimonides suggests bribing him with sweets or nuts. When they are a little older, he recommends giving the child money. Older still, honour. When they mature, he advocates promising them the World to Come. And if they finally get it - they will do the right thing because it is the right thing - without any ulterior motive.

Similarly, when it comes to discipline - when a child is young, corporal punishment is at times in order. As King Solomon, the wisest of men, says in Proverbs: One who withholds the staff, hates his son. Yet the Code of Jewish Law says that hitting an older child is a grave sin. Clearly what is appropriate at one stage of our relationship with our children is totally inappropriate at another.

Moses' error in hitting the rock underscores how failure to adapt to changes in our relationships comes at our peril.