When Jews were crossing the sea, two events happened. One: the Heavens descended down to the Earth. Two: the Earth was elevated up to the Heavens.
Alter Rebbe explains in a ma'amor that sea represents G-d's Speech, which is the sphera of Malchus of Atzilus. All three concepts — sea, speech and Malchus — have in common that they exist both to unite and to separate. (Interestingly, this is also the idea seen in the mitzva of Havdala.)
In order to express his thoughts to others, a person must speak. But at the same time, speech separates the one who receives the person's ideas from the person's mind. Once spoken, thoughts do not exist anymore in the same state as they did in the mind. They are made accessible, crystallized — and also limited.
Similarly, the sphera of Malchus of Atzilus exists to create the lower worlds, to direct to them the light of its own world — but at the same time, Malchus separates the three created worlds from Atzilus.
In this way, it is also similar to the sea. Malchus is called "the great sea", because, just like "all rivers fall into the sea", the six emotional spheros (Ze'er Anpin) collect their lights into Malchus. And just like the sea separates the marine creatures from the earth creatures, since the former cannot breath above the water and the latter cannot breath below it, Malchus of Atzilus makes sure that the phenomena of Atzilus cannot exist in the created worlds (they would "suffocate" from such limited Light) and that, conversely, the created beings cannot ascend into Atzilus (since they can only receive the Light in a limited form through the vessels of their worlds and would "dissolve" in Atzilus).
This, then, was what happened during the Kriyas Yam Suf, the splitting of the Sea of Reeds: the Great Sea, Malchus of Atzilus, split. Two views (that of the Zohar and that of Arizal) exist regarding what happened:
- The limitation of Malchus of Atzilus was stopped so that the Lights of Atzilus could descend and unite with the physical universe below and Jews inhabiting it.
- When Malchus "split", the Jews were elevated into Atzilus.
One of the views places emphasis on the fact that the Jews were able to continue walking on dry land towards their destination. If there was a sea on their way — then the sea split, but that's not the main point. The other view's emphasis is on the fact that Jews were plunged into the middle of the sea. The dry-land aspect of the journey was only a means for the Jews to survive their journey into the realm normally uninhabitable.
Alter Rebbe explains in his ma'amor that both these points of view are correct: the Heavens split and the Supernal Lights were able to reach the physical Universe and the Jews, and, at the same time, Jews themselves were elevated to the level of the Supernal Lights.
Kriyas Yam Suf was an event that prepared the Jews for the receiving of Torah. The two spiritual aspects of the Splitting corresponded to two aspects of Mattan Torah: the fact that it was received (by Jews) and the fact that it was given (by G-d). On the one hand, Jews are never lofty enough to receive the Wisdom and Will of HaKodosh Boruchu Himself. On the other, G-d is too lofty and elevated above the physical aspects of the world for His Will to be associated with them. Both these limitations (so to speak) were broken at the Kriyas Yam Suf.
This explains what Torah and mitzvos accomplish. On the one hand, they elevate the person who performs them to the state of holiness ("asher kideshanu bemitzvoisav..."). On the other, they introduce G-dliness into the physical aspects of the world and the levels of our souls associated with them, creating a dwelling in the lower worlds for G-d.
On the more abstract level, the two aspects correspond to yichuda ila'ah and yichuda tata'ah: the Upper Unity and the Lower Unity. The first is the concept that ein od milvado — there is nothing but G-d, in a simple, literal sense. Even though on our level of reality, the worlds exist, in relationship to G-d's Essence, nothing exists. (Imagine this as the function of y = 1/x taken to infinity. The larger the x, the smaller the y — but still always finite. But when x = ∞, then y = 0, mamosh.) And obviously, our point of view is "wrong" when compared with G-d's point of view. On the ultimate level of truth, nothing but G-d exists.
The concept of Lower Unity corresponds to the idea of G-d's unity with all of creation. From this point of view, all of the worlds exist, but they are still completely one with G-d, in a perfect (albeit complex) unity. This is revealed by the fact that He creates them all every single moment (or, to put it more correctly, He creates their every moment). That His thought pervades them all. That for Him, they exist as one point, with all dimensions compressed into a single idea.
For our avoida, this means that two levels of bittul exist. These two levels are represented by two colors of flame (and two colors of tzitzis strings): white and blue. Flame is a symbol of bittul: the desire of the soul to "rise" and nullify itself to G-d. There is the "blue" level, the part of the flame that hugs the wick. Then there is the white level, the part of the flame which never even touches the wick.
In our lives, the blue flame corresponds to the idea of realizing and revealing G-d's omnipresence in our lives (on the one hand, the flame rises from the candle; on the other, it is still connected to the wick). The fact that everything that happens in our lives is connected to G-d and is only due to G-d's Will and Kindness. And, respectively, that everything that we do in our lives must be connected to G-d. We cannot do anything "stam". Everything must be, one way or another, an aspect of avoidas Hashem.
And then there is the level where nothing but G-d exists. This level is achieved in our avoida through contemplation about G-d, as we learn about Him in Chassidus, during davening, on Shabbos and holidays. On this level, not only is G-d one with the world, but G-d is One — the only one.
As Alter Rebbe's ma'amor teaches, both aspects are extremely important and both aspects are the part of our journey to Har Sinai — to the point in the world's history, where G-d's Essence will be revealed. And this time, not for a short time only, as it happened during Mattan Torah, but forever. May it happen speedily in our days.