From the upcoming MeOros Kedushas Levi in English:
Parashas Chukas
The Way to Give Rebuke
You shall speak to the rock before their eyes that it should give its waters... And he raised his arm and struck the rock... And Hashem said to Moshe, "Since you have not believed in Me in order to sanctify Me before the eyes of the children of Israel, you will not bring this congregation to the land that I have given them."
(Bamidbar 20:8–12)
Rashi and Ramban disagree regarding what Moshe's sin was. One [the Ramban in the name of the Rambam] explains that his sin was that he said to the people, "Listen, you rebels!..." The other comments that his sin was striking the rock. It seems to me that these explanations are really one and the same, because one led to the other.
There are two ways to rebuke a Jew so that he will fulfill the will of the Blessed Creator. One way is to speak nicely and pleasantly — one tells the Jew how great he is and where his soul was made, that it was hewn Above under the Throne of Glory,6 and of the great pleasure that the Blessed Creator derives from the mitzvos of each Jew, and of the great joy that permeates all the worlds when a Jew performs the mitzvos. With this form of rebuke, one can convince a fellow Jew to fulfill the will of the Creator and accept upon himself Hashem's kingship.
The other way is to speak sharply and shame the person into doing the will of the Creator. The difference is that the one who uses kind, gentle words elevates the Jewish soul higher. He tells stories of the righteousness and greatness of Klal Yisrael, how great is their power up above in Heaven. A person who rebukes this way is worthy of being a leader of the people. But the one who uses sharp words is not in this league [and is not fitting to lead].
When one rebukes with kind words, constantly telling stories of Klal Yisrael's greatness and righteousness, then all of creation fulfills the will of the Jewish people of its own volition, since this is the purpose for which it was created — for the sake of Klal Yisrael [so that they could fulfill their purpose in this world, which is to serve Hashem].7 However, when one does not talk about Klal Yisrael's greatness, then the creations must be forced to perform its function and fulfill its purpose.
When Moshe said, "Listen now, you rebels!" He rebuked the Jewish people with harsh words, and therefore he needed to strike the rock so that it should perform for him as it was meant to perform. Had he instead elevated the people [through gentle words], as we explained, which is what HaKadosh Baruch Hu was telling him to do — "You shall speak to the rock" — then he would have said the following to the rock: "You who were created for the purpose of serving Bnei Yisrael, who are on such a high lofty level, must do the task for which you were created and give forth water for the people." However, since he rebuked the people with harsh words saying, "Listen, you rebels!" he had to strike the rock to force it to perform Bnei Yisrael's will.8 Thus we find that one sin caused the other.9
We see this from our verse, "Since you have not believed in Me in order to sanctify Me before the eyes of the children of Israel..." The one who rebukes Klal Yisrael with nice words can give over this ability [to likewise rebuke with kind words] to the nation. This is hinted at in the word l'einei, "before the eyes" — that he could literally sanctify the "eyes" of the congregation, as our Sages taught, " 'The eyes of the congregation' refers to the wise men of the congregation" (Shir HaShirim Rabbah 1:15),10 so that they will also be able to acquire this ability.
The Maggid's Promise
Once, a maggid came to Berditchev seeking to raise money to marry off one of his daughters. He went to Rav Levi Yitzchak for permission to speak in the beis midrash. The Berditchever gave him permission on one condition: he was forbidden to speak disparagingly about the holy children of Israel during his speech.
In the midst of his sermon, the maggid got carried away and forgot his promise. He began to rebuke the people with sharp words. When the Berditchever heard this, he ran up to the aron kodesh and opened its doors, pleading: "Ribbono shel olam! Master of the world! Do not believe what this man is saying! Give him the money that he needs to marry off his daughters. Just do not let him speak negatively about Klal Yisrael!"
