Musar zu Schemot 13:4

This is hinted at in Exodus 13,4, היום אתם יוצאים בחודש האביב, "Today you are leaving, in the month of spring." The word "today" in this context seems superfluous. I have heard that the meaning is that on that day the sign of the Aries begins its ascendancy, signifying to Israel and to Egypt its helplessness against Israel. This is stressed since the appearance of that sign does not always coincide with this date. Sometimes it appears a day sooner, sometimes a day later. The Torah emphasizes that in that year the appearance coincided with the date of Passover, i.e. on the fifteenth of the month. The end of its dominance in the sky therefore, was on the 14th of lyar. Though this is not typical of most years, the determining consideration is the commencement, the root, as I explained elsewhere. Normally, Aries commences on the day of the spring equinox. In the year of the Exodus the sign of the ram took up its position in the sky starting on the fifteenth of Nissan. As a result of all this the 15th of ניסן and the 15th of אייר share something significant, so that it is logical that the observance of the "second" Passover should be fixed to occur on that date.

As a result of benefitting from all those miracles, the ערב רב were required to celebrate the Passover and to observe all the prohibitions connected with the leavened bread. You have already been made aware that the ערב רב do have a mystical bond with the emanation דעת עליון, or בינה. The mystical dimension of the מלכות של בינה contains the secret of the significance of המצה השמורה העליונה which is symbolised by the enlarged letter ד in the word אחד of Deuteronomy 6,4, as I have explained when discussing the deeper meaning of that מצוה. This is why the Jewish people were commanded to eat unleavened bread. This is also where you find the secret of why the Talmud (Shabbat 33) considers נשים דעתן קלה עליהן, "the minds of women are shallow." The numerical value of the word מצה is 135, the same as of the word קלה. Moses said to the ערב רב: "You are leaving Egypt this day," היום אתם יוצאים ממצרים. The reason Moses added these apparently superfluous words was to make them understand that there is one commandment which will be addressed only to the children of Israel and not to them. They should not be surprised at this, since they did not need this commandment; G–d did not select them as His people. They had already been given the commandment of מצה because that commandment had a significance which related to them. The reason that the original Jewish people needed the commandment of sanctifying their first-born was that G–d saved the first-born of the Jewish people when He slew the first-born of the Egyptians. An expression of eternal gratitude by those who were spared was indicated as a result. The ערב רב had not been spared; those surviving had joined the Jewish people only on the morrow at the time of their departure, i.e. היום!