Moving beyond how the ideas are transmitted to the content itself, boy, do I feel sorry for you uber-Litvaks. For those who know the Rav's biography and other writings, the fact that he would use an idea he took from his Chabad melamed is already to be expected. The Kotzker vort thrown in to make a point can be dismissed as a rhetorical aid; the R’ Nachman story about the heart and the river the Rav references is well known and I would not make too much of it. Yet aside from these references, many of the ideas the Rav uses are already found in sifrei chassidus. For example: his interpretation of the burning bush as the flame within can be found in Sefas Emes; the idea of “Vaeschanan” being a lonely prayer that might have been accepted had Klal Yisrael joined in is in the Ishbitzer; the idea of “boker” as signifying clarity and not just a time is in the Shem m’Shmuel. Do I think the Rav borrowed the ideas from these sources? No, not at all. I would be shocked if someone told me the Rav read Ishbitzer torah. I think the Rav independently arrived at the same ideas. The point is that one cannot be dismissive of chassidus while at the same time accepting the same ideas just because they came out of the mouth of the Rav. And instead of waiting for techiyas ha'meisim to hear similar ideas presented by the Rav in his own special style, if one wants more of the same (albeit in different language and style) one can broaden one's horizons and dive into the Sefas Emes, the Shem m'Shmuel, etc. in the here and now. It won’t hurt – trust me.
Along the same lines, what does the modern Orthodox community make of the Rav's assertion that the authority of Torah scholars is even greater than malchus? Sounds like a position I would expect the staunchest adherents of da’as Torah to argue!
Getting to something from our parsha, the Rav suggests that there are two different aspects to kedushas yisrael: there is kedusha that is generic and covers equally everyone who associates with the Jewish nation, and there is a kedusha that is unique to each individual. He reads the pasuk in our parsha, “Ki am kadosh atah… u’becha bachar Hashem l’heyos lo l’am segulah,” (14:2) as defining this multi-tiered kedusha: Bnei Yisrael is a holy nation, i.e. there is a kedusha to the collective group, but also, “becha,” you, the individual, has been chosen to make (l’heyos=create) the nation special by contributing your unique talents.
The Rav connected this dual-kedusha to the two steps in the process of geirus, milah and tevilah. Milah associates the individual with the nation; tevilah is a process of personal kabbalah.
The Rav saw Korach’s rebellion as a failure to realize these two levels. Korach argued, “Ki kol ha’eidah kulam kedoshim,” everyone is holy, everyone is equal. If one looks at the collective unit of the nation, than indeed, we all are equal members. But what Korach did not realize is that in addition to the collective holiness of the group, each individual Jew has a personal level of kedusha that is unique. Moshe Rabeinu does not in that regards share the same kedusha as Moshe the woodchopper.