Moses struck a rock twice and water issued forth. Once in Parshat Beshalach and again in Parshat Chukat. In Parshat Beshalach G-d desired a physical strike – even commanded it. In Parshat Chukat, though, G-d didn’t want the latter but rather that Moses speak to the rock (according to Rashi). If the miracle in Parshat Beshalach was effected via striking the rock, why 40 years later, here, in Parshat Chukat, was the miracle not to be carried out in the same way?
Though we can answer this in a number of ways, let us adopt one approach. Since the miracle of striking the rock had already occurred & was well known, its repetition, despite the passage of 40 years, would not have had such a great impact. Thus there was a need for a different miracle.
This principle I learned from the Meshech Chochmah in a different context – that of Splitting the Reed Sea. The Midrash says that in the future G-d will perform more miracles for Israel in the World to Come than He did at the Splitting of the Reed Sea. The Meshech Chochmah is puzzled – were the latter miracles insufficient ? He answers that after the Israelites had seen these miracles, there was a need for greater miracles to arouse their wonder. He gives the example of the telegraph, explaining that once people became accustomed to it, they weren’t all that impressed with the telephone which followed it.
The Mechilta at the end of Chapter11 comments on (HaShem) does wonders. He did wonders for the fathers and in the future will do so for the children, as it says "As in the days of your coming out of the land of Egypt, I will show him wondrous deeds.’ (Micah 7:15) – I will show him what I did not show the fathers. A wonder – a miracle- means something which boggles the mind, which a person cannot credit until he sees it with his own eyes. Thus with the invention of the telegraph – it amazed the beholders’ imagination. It was indeed a wonder. Afterwards, with the invention of the telephone, which required far greater expertise, people were not as amazed as they had been with the telegraph.
So, with the miracle of the Sea Splitting and the wonders of the Manna and the Slav, everyone was amazed. The Navi now says that since the splitting of the Sea and the Manna were already known as the fathers had them, in the future G-d will do things which will awe the children anew. Then the Sea splitting and the Manna will be like the natural order. Thus afterwards there will be no comparison between what the fathers saw with what the children will see. From my grandfather Harav Chananya Zt"l.
And so too in our Parasha. The miracle of bringing forth water by striking the rock was indeed most impressive, but after the Children of Israel saw this miracle, they were not so amazed when it repeated itself again. So there was a need for a greater miracle – one of speech.
We experience so many miracles, so much Divine goodness in so many things, we often fail to appreciate the enormity of the salvation which G-d brings us, all the time. Occasionally we need to go back and observe, to feel all of G-d’s kindness "For Your wonders and favors are with us in every season" and from observing G-d’s kindness, we will always remember "It is good to thank G-d".