From Chapter 8 of Rabbi Shloma Majeski’s Likkutei Mekoros (Underlined text is the compiler’s emphasis.)
Translated by Boruch Merkur
16. […] Our avoda (stemming from the lower realm) is relevant to even the Rebbe himself (the higher realm).
Consider the story about how the Chassid Reb Yaakov Mordechai from Poltava went into yechidus with the Rebbe Maharash, and the Rebbe told him, “When there is a Rebbe, there are Chassidim. That is, Chassidim that are active in avoda.” And he concluded, “And the Chassidim, by being Chassidim and by being accomplished in the realm of the service of the heart [prayer] – they gave strength to the Rebbe [referring here to the Alter Rebbe].”
From this account we understand the great responsibility of a Chassid who is connected to the Rebbe. A Chassid’s conduct has an impact upon the Rebbe himself. In fact, when a Chassid behaves in an undesirable fashion, G-d forbid, he not only “harms himself” – in which case he would be deemed unworthy, but exempt from punishment – he “harms others” as well, in which case he is liable. How much more so in our case, when “others” refers to the general soul [i.e., the Rebbe], etc., etc. – for then the liability is much greater.
17. On the verse at the beginning of this week’s parsha, “And the years of Sara were a hundred years and twenty years and seven years,” our Sages teach: “‘Years’ is repeated here to describe each phase of Sara’s life, telling us that each is to be interpreted individually – Sara at 100 was like a 20-year-old…and at 20 she was like a girl of 7.”
The practical application of this teaching:
“100 years” is the age associated with the completion and perfection of one’s service of G-d. That is, when all ten soul powers include and branch off into ten, the aggregate of which is, of course, 100.
“20 years” is the age when the avoda as an adult begins. An adult, a gadol, is one who possesses mochin d’gadlus, a mature and developed mind. (Although Torah recognizes various stages of a minor, true adulthood begins at age 20.) It is for this reason that one who has not reached the age of 20 may not be involved in the sale of the estate of his father. Also, the Alter Rebbe rules in Laws of Torah Study that by the age of twenty one has attained (not only five years of Mikra, Scripture, and five years of Mishna, but also) five years of Talmud, and then it is time to pursue a livelihood (“at age twenty, one pursues” ––Avos Ch. 5, end).
The reason for this law – that a twenty-year-old must pursue a material livelihood – is because that is the case with regard to a spiritual livelihood (as stated several times that the laws in the revealed, legalistic dimension of Torah derive from the inner dimension of Torah). Indeed, Chassidus explains that since the soul yearns for the spark of holiness found in food [for example], the body also becomes desirous of food.
“And 7 years” is the beginning of the age of education.
In light of the above we can explain the teaching that “Sara at 100 was like a 20-year-old…and at 20 she was like a girl of 7”: In order to achieve the perfect avoda of “a hundred years” in a manner of “Sara at 100 was like a 20-year-old” – that even at the final stage of avoda it should be “without sin” just as at the beginning of the avoda – there must be “at 20 she was like a girl of 7.” That is, even at the age of 20, when one attains mochin d’gadlus, one should not have his own opinions. Rather, he should behave like a seven-year-old, one who has no opinions of his own; he merely does as told.
Even a twenty-year-old, who has (or at least ought to have, and therefore thinks he has) mochin d’gadlus, should not make his own pathways. Each person must accept upon himself – according to his own reckoning – something that the Rebbe used to demand of him, and he must fulfill that and complete that mission.
(From the address of Shabbos Parshas Chayei Sara, Mevarchim HaChodesh Kislev 5711; Toras Menachem 5711, pg. 94-95)