What is easier: keeping a powerful beast like a cow or a bull locked up in it’s pen, or a bird? Which requires “additional guarding”?
Although a bird possesses nothing of the power that the bull has, it has an additional ability that even the most powerful beast lacks — the power of flight. Thus, fences are sufficient to keep a mighty bull locked up, but a tiny bird is not properly guarded unless the walls are capped by a roof.
In Halocho this expresses itself in the laws regarding courtyards — that a large courtyard that is not covered by a roof is considered a carmelis (by Rabbinic decree, even though according to Torah it is a private domain (reshus hayochid)), but if it is covered with a roof then it remains a private domain according to Rabbinic opinion as well.
The maamor printed for 18 Nissan, 5751 (anniversary of the Rebbe’s Bris Mila) explains this in terms of our Divine service: the animal for which fences are sufficient is our animal soul; the bird that requires a roof is our Intellectual Soul (Nefesh Hasichlis). The animal soul, while powerful, has four legs on the ground and looks down — it’s only attraction and interest is gashmiyus. It is enough to build fences to pen it in. But the Nefesh Hasichlis, while it is a human intellect which relates to worldly things, possesses an inclination to “fly away” to contemplate things which are of a higher nature. Thus it needs a roof as well.
What is this roof?
In our Divine service, the “roof” is the wonderment (הפלאה) we feel when contemplating and realizing that the lofty things we are studying (and through study, grasping) are in fact beyond our grasp because they are G-dliness. G-dliness is without bounds, but whatever we understand with our human intellect (the Nefesh Hasichlis) is limited, and thus or understanding is not the “real thing”. Keeping this in mind puts a “roof” of self-nullification (bittul) on our intellectual efforts so they don’t get carried away with themselves and “fly off” from the realm of the Oneness of Hashem (reshus hayochid) and enter the realm of self-importance and pride (ישות וגאווה).
How does this relate to our Sichos of 5751-52?
The avodah of Chassidim since the revelation of Chasidus was primarily in the realm of emotional attributes (midos) — battling and striving to transform the animal soul. Learning Chassidus was a major component of this avodah, but the revelations of Chassidus kept to the boundaries of Torah and Mitzvos — Tikkun.
In the Sichos of 5751-52, when the Rebbe will demand “do all that you can to draw down the lights of Tohu (but in a way of vessels of Tikkun)”, the revelations cross the border from the Torah and Mitzvos of the time of golus (limited, but familiar to our human outlook and understanding) to the first stage of the Messianic era (ימות המשיח) and elevate us to a new (and unfamiliar) level of understanding and a new outlook.
The work of transforming the animal soul, the Rebbe informs us, is completed (and if we don’t see this, it is only because we haven’t made the proper effort to reveal it), and we begin the shift to transforming our consciousness, the realm of the Intellectual Soul.
So right from the beginning of this seismic shift in the pnimiyus of our avodah, the Rebbe published this maamar to give us a “heads up” that while keeping the behema (the animal soul) only required fences, the next step of “opening the eyes” of the Intellectual Soul requires a roof as well if we are to keep ourselves within the private realm, the “reshus hayochid“.
Internalizing concepts such as: we can now “fill our mouths with laughter”; we have reached the time for receiving the reward of our Divine service; Yidden and Hashem are really One thing; Mitzvos will be nullified in the future; the created “yesh” is in essence the true “Yesh” of Hashem’s essence; etc., require one to “cover” his intellectual efforts in these concepts with a “roof” of bittul so that his Intellectual Soul will not “fly away” and take these ideas to the wrong place.
(We could further say that through this discourse the Rebbe gave Chassidim the power to do this lechatchila, and to understand the Sichos in the proper way, consistent with Halacha — as we see is the case across Lubavitch!)