The battles fought between the Jews and their enemies, which took place on Adar 13 throughout the Persian empire (see "Today in Jewish History" for that date), continued for two days -- Adar 13 and 14 -- in the capital city of Shushan, where there were a greater number of Jew haters. Thus the victory celebrations in Shushan were held on the 15th of Adar, and the observance of the festival of Purim was instituted for that day in Shushan and all walled cities. (See Laws and Customs below).
On this date, in the year following the Holy Temple’s destruction, G‑d tells Ezekiel to take up a lamentation for Pharaoh, king of Egypt, and for the Jewish nation’s other enemies, foretelling their ultimate downfall.
Read the prophecy here: Ezekiel ch. 32
In cities that are surrounded by a wall dating from the days of Joshua (13th century BCE) -- a prominent example is the city of Jerusalem -- the festival of Purim is observed on the 15th of Adar (instead of the 14th), in commemoration of the fact that in the ancient walled city of Shushan, the first Purim was celebrated on this day (see "Today in Jewish History").
All over the world, Tachanun is omitted due to the special joy of the day.
(For an overview of the Purim observances and links to more information, see "Laws and Customs" for Adar 14.)
Take these words of Mine to your hearts and to your souls…teach them to your children so that this will be what they speak about, when you are sitting at home, walking on your way, lying down to rest, and arising from your sleep. (Deuteronomy 11:18-19)
The simple meaning of this instruction is as follows:
You must teach your children Torah.
Not as a burden, but as a love; so that they will cherish Torah wisdom, share it, and speak about it at every time of day, in every circumstance. Until it becomes the defining activity of their lives.
And to accomplish this, you too must be engaged, heart and soul, in your children's education the entire day.
Not only at home, when you are in your own space, but even when you're off at work or in other circumstances you do not control, this is what should preoccupy your mind.
So that when you lie down to rest after a long, hard day, the concern won't go away.
And when you awaken refreshed in the morning, your first thought will be, "What's happening with my children's education?"
This is why there are Jews today, how this miracle occurred: Because there were Jewish parents who focused their entire lives on the Torah education of their children.