The Shabbos of Parshas Tazria-Metzora 5751 was the first time that one of the Chassidim (R’ Dovid Nachshon) worked up the nerve to declare “Yechi…melech Hamoshiach” before the Rebbe (see “The Facts Behind the Psak” for details), and therefore we are presenting a free-translation of the relevant passages from the sicha of Beis Nissan, 5748, where the Rebbe himself introduces and explains the significance of the declaration “Yechi Hamelech”. (Bold emphasis in the original sicha):
…the heart is the life-force of the body itself, being that it is the location of “the blood, which is the soul”, and the heart causes “the dispersion and circulation of the life-force…which is enclothed in the blood of the nefesh which goes out from the heart to all of the limbs, and circulates the life energy (“ruach chayim“) and the blood into every limb and the ligaments and it is absorbed by them and returns to the heart, etc.” (as the Alter Rebbe explains in Igeres Hakodesh, ch. 31).
So it comes out that the important element of the life-force of all the limbs of the body are connected with the heart, since the blood (“which is the soul”) which is in the heart…is actually dispersed to all the limbs of the body.
Life-force is connected with movement. And movement is found specifically in the heart, for it is found to be constantly pumping and drawing blood, “the pulse of the heart”. And the blood that is in it is also in a constant state of movement, circulating throughout the entire body (as explained in Igeres Hakodesh), which is not the case with the liver and the brain [two other essential organs mentioned previously] which do not move.
Similarly this is true as regards the Leader (the Nosi) and the King (the Melech), “the heart of the community of Israel” (Rambam) — “who sends them out and brings them back”, meaning that in accordance with his word comes about (as well — in addition to the head and the brain which provide guidance and direction) the drawing down of life-force to Bnei Yisroel.
And when the day arrives which was the beginning of the leadership (Beis Nissan [the day the Previous Rebbe became the leader upon the passing of his father, the Rebbe Rashab]), there is an increase in the aspect of the heart, meaning and increase in the matter of the life….
4) …on the one hand, the dimension of loftiness and separateness, [that the King is] “head and shoulders above the rest of the nation”, specifically “nation”, “from the word meaning ‘individual coals’, that they are things which are separate and foreign and distant from the level of the King.” This is emphasized in the degree of awe and self-nullification (bittul) to the King — “place upon yourself a King” which the sages explain as “place awe of him upon yourself”.
On the other hand — the ultimate closeness, as has been stated, that the King is “the heart of the entire community of Israel”. For there is no greater closeness than the closeness of the heart to the limbs of the body, as was explained that the blood in the heart itself is found constantly in all of the limbs: “the dispersion and circulation of the blood to all the limbs is constant…that all the limbs are connected together and receive their life-force from the heart.”
And more than this:
The closeness between the King and the nation is not only as regards to dispensing life-force to the entire nation, who receive their life-force from the King, but rather also the opposite — that the existence of the King is dependent upon the nation, “there is no King without a people“, which means that even though they are called a “nation, from the word meaning ‘nearly extinguished coals’…distant from the level of the King.”, nevertheless at the same time (and, in fact, because of this) they are the cause of the Kingship — the King.
And this is emphasized in the crowning of the King — that the people declare “Yechi Hamelech” [“long live the King”] (as we find also in the Kingship of the House of David), that in this is emphasized as well that the actions of the people are in the King’s life, the life of the King.
5) …in addition to what was said regarding an increase in life to all people in the generation via the Leader of the Generation, the Nosi Hador — it is also true that the people of the generation cause an in crease in the matter of life to the Nosi Hador, as was stated above regarding the declaration “Yechi Hamelech”.
In simple words:
After we have completed 68 years (numeric value = “life”) of the leadership (his activities and his efforts) of Nosi Doreinu — there needs to be an essential increase in the inyan of the life (also) via the actions of the people who declare “Yechi Hamelech”, the meaning of this declaration being — that we have already arrived at the time of “arise and sing those who dwell in the dust” — my father-in-law Nosi Doreinu and until the arise and sing Dovid Malka Mashicha!
And this is also the “shturem” that is made at the time of ikvesa d’Meshicha [the heels of Moshiach, the final stages] regarding the need to declare “ad mosai” [“Until when?!”], for through this we bring closer and speed up the Geuloh. And we can say that in addition to the emphasis on anticipation, the request and the demand for the Geuloh [which brings Moshiach in actuality, in a way that one can point with his finger and say ‘this’, here is the Melech Hamoshiach, flesh and blood, as ruled by the Rambam “a King will arise from the house of David…and will gather in the exiled of Israel”], in this declaration is included the intent of Coronation — “Yechi Hamelech”, that through this we bring about the coming of Dovid Malka Mashicha.
6) Additionally, regarding Melech Hamoshiach it is emphasized even more his relationship to every single member of the Jewish nation (in addition to the fact that every King is “the heart of the entire community of Israel”) — therefore, every single individual possesses the power and the ability to bring about the matter of “Yechi Hamelech”.
I think it’s important to note that the Rebbe made a hand-written change to the sicha to indicate this specifically applies to the time after Rebbe’s the apparent histalkus.