Why was Moshe Rabeinu punished for striking the rock, rather than speaking to it?
And the LORD spoke unto Moses, saying: ‘Take the rod, and assemble the congregation, thou, and Aaron thy brother, and speak ye unto the rock before their eyes, that it give forth its water; and thou shalt bring forth to them water out of the rock;
I saw in the book, Aizor Eliyahu, collected sermons of Rav Eliyahu Lehrman of Viskit, a student of the Kotzker Rav, that the gematria of the word סלע (rock), 160, equals that of the word כסף [kosef] (longing, aspiration) as in the verse: נִכְסְפָה וְגַם כָּלְתָה נַפְשִׁי לְחַצְרוֹת יְ-וָה.
And a thought entered my head.
What was the reason that God ordered Moshe to speak rather than to strike the rock?
He was seeking a spiritual uplifting result so that the children of Israel would be encouraged to overcome temporary physical difficulties, that despite the very real problems, such as thirst, a strengthening of the will is essential, especially as they were now about to enter Eretz-Yisrael and a vision was what would carry them through to victory.
Striking the rock, instead of speaking to it, was not the example that God wished for Moshe to present. He was to simply speak to it, just like he would soon be speaking to the children of Israel to exhort them to enter then land, to wage war and the settle it.
They needed to be uplifted, to be able to see beyond the physical. Moshe did not supply that example.
Comprehended this way, we can also understand the severe punishment meted out to Moshe, that he will
not bring this assembly into the land which I have given them.
If the ultimate goal of speaking to the rock was part of the preparation for entering the Land of Israel, then the preventing of Moshe from entering is the fit punishment.