After seven days of contention with G-d at the burning bush (see entry for "Nissan 15"), Moses assumed the mission of taking the Children of Israel out of Egypt. Taking leave of his father-in-law, Jethro, he placed his wife and children on a donkey and set out for Egypt to demand of Pharaoh, "Let My people go!"

On the eve of the seventh day after the Exodus, the Children of Israel found themselves trapped between the Egyptian army and cavalry pursuing them from behind and the waters of the Red Sea before them. G-d commanded Moses: "Speak to the Children of Israel, that they should move forward!"

Nachshon ben Aminadav of the tribe of Judah was the first to jump into the sea; the water split, and "the children of Israel walked across on the dry land in the midst of the sea." All that night, a pillar of fire intervened between the Egyptians and the Israelites. When the Egyptians followed, the waters returned to their natural state and place and drowned them. The Children of Israel sang the "Song at the Sea" in praise and gratitude to G-d.

Links:
The Exodus, Part II
Murky Depths
more on the Splitting of the Sea

On the Seventh Day of Passover we read how on this day the sea split for the Children of Israel and drowned the pursuing Egyptians, and the "Song at the Sea" sung by the people upon their deliverance (Exodus 13:17-15:26; full summary with commentary here).

Unlike all the other festivals, only the abridged version of Hallel (Psalms 113-118, recited on special occasions in praise and thanksgiving to G-d) is said on the latter days of Passover. The reason for this is based on the Midrash which relates that when the Egyptians were drowning in the sea, the angels in heaven desired to sing; but G-d said to them: "The work of My hands is drowning in the sea, and you wish to sing?"

Tomorrow is the seventh day of the Omer Count. Since, on the Jewish calendar, the day begins at nightfall of the previous evening, we count the omer for tomorrow's date tonight, after nightfall: "Today is seven days, which are one week, to the Omer." (If you miss the count tonight, you can count the omer all day tomorrow, but without the preceding blessing).

The 49-day "Counting of the Omer" retraces our ancestors' seven-week spiritual journey from the Exodus to Sinai. Each evening we recite a special blessing and count the days and weeks that have passed since the Omer; the 50th day is Shavuot, the festival celebrating the Giving of the Torah at Sinai.

Tonight's Sefirah: Malchut sheb'Chessed -- "Receptiveness in Kindness"

The teachings of Kabbalah explain that there are seven "Divine Attributes" -- Sefirot -- that G-d assumes through which to relate to our existence: Chessed, Gevurah, Tifferet, Netzach, Hod, Yesod and Malchut ("Love", "Strength", "Beauty", "Victory", "Splendor", "Foundation" and "Sovereignty"). In the human being, created in the "image of G-d," the seven sefirot are mirrored in the seven "emotional attributes" of the human soul: Kindness, Restraint, Harmony, Ambition, Humility, Connection and Receptiveness. Each of the seven attributes contain elements of all seven--i.e., "Kindness in Kindness", "Restraint in Kindness", "Harmony in Kindness", etc.--making for a total of forty-nine traits. The 49-day Omer Count is thus a 49-step process of self-refinement, with each day devoted to the "rectification" and perfection of one the forty-nine "sefirot."

Links:
How to count the Omer
The deeper significance of the Omer Count