Let me begin my answer with a story that the Rebbe told at a Farbrengen..
“A few days ago, a young man walked in to [my room] and told me excitedly that he [once] told my father-in-law, the Rebbe [Rayatz] that he wants to connect to the Alter Rebbe. The Rebbe answered him, “Zay mekusher tzu mir, vestu bemeila zain mekushar tzu di mit veleche ich bin mekushar” – that by being bound to him, he would thereby be connected to those whom he (=the Rebbe himself) was bound….
The Rebbe went on and said: “I did not want to cool his enthusiasm, but the truth is, that to whom the Rebbe is bound is not our concern. We are bound to him, and we have nothing higher than that.” (2 Iyar 5710, translated into English in “Proceeding Together” vol. 1)
Now, this story is not about going to Rebbeim of other Chassidic groups; in fact, it makes a much more sensitive point:
A Chassid of a Rebbe has no interest other than his Rebbe, not even his Rebbe’s Rebbe! Not because his Rebbe is greater than any other Rebbe (because who is he to measure the greatness level within our seven Rabbeim?); and not because he doesn’t care about any other Rebbes, rather because the relationship between a Chassid and a Rebbe is so deep and meaningful, that nothing else matters.
To be clear: this is not about elitism; we are not going around and tasting different kinds of food to show that ours is the best one… The connection of a Chassid to the Rebbe is an essential connection through which the Chassid connects to Hashem [and once that relationship is established,] I don’t even consider entering into any other relationships.
A Chassid has his Rebbe, and that’s it! He has no interest in anything else, even on a spiritual level. He might learn Torah from many others and gather ideas from others, but as far as a “Rebbe” is concerned – in the sense of he who teaches you how to connect to Hashem, and who practically and spiritually is the link between your Neshama and Hashem’s essence – there is only one!
There are many stories about Chassidim who were in dire need of salvation, pikuach nefesh mamash, and refused to go and even ask for a b’racha from another Rebbe!
The Rebbe said: “Bei mir, hecher fun der shver is nitto – to me, there is no one higher than my father-in-law.”
He wasn’t saying this to be a purist or radical, he was saying in other words: I’m a Jew and a servant of G-d, and for this, I need a Moshe, a Rebbe. I’m not a “nosher” being curious and “checking out” other places. I’m in the business of having a relationship with Hashem, my Rebbe is that entire relationship, and there is nothing beyond that.
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So, what does this story reveal?
It’s twofold: the obvious part which is always noticed is that the truth is that a Chassid has a Rebbe, and besides that, he doesn’t care for any other relationship. But the same story teaches us that we may not take away from someone else’s inspiration, as the Rebbe said “I did not want to cool his excitement…”
Some go to other Rebbeim’s “tish” out of curiosity; some go out of respect and deference, and some go to be inspired.
There is an ideal relationship between a Chabad Chassid and the Rebbe, but the ideal and the practical are not always the same thing, and if a Yid is inspired [in not the ideal way, but still inspired] to be a better Jew, you must think a hundred times before taking away his inspiration!
In other words: are you prepared to inspire that person? Are you able to supplement and to provide the inspiration you are taking away from him by telling him don’t go here or there?
Yes, the goal and ideal of Hiskashrus is to have that deep relationship where even considering connecting to another Rebbe would be absurd, but the practical answer to this question depends very much on where the person in question is holding.
Transcribed and edited from a video on StumpTheRabbi.org