The Hebrew Month of Nissan went to the Heavenly Throne to complain that, as the first month of the Jewish year, it should have Jewish New Year, Yom Kippur, the Festival of Booth, and the Festival of Simchat Torah. Why are they in the Seventh month, Tishrei? The L^rd tried to pacify it.
You have Pesach, the most popular Festival of all. With the eating of the Passover lamb, the most important Jewish eating of the year. And the commemoration of the Liberation out of Egypt, the Splitting of the Sea, and the birth of the Jewish People. The greatest events in history after the Creation of the World, and the strengthening of the greatest upcoming event ever, total Redemption for everyone.
And, I will give a semi-festival that will be almost as popular as Passover. That will stand with you as it is not even written in the Torah and alongside Simchat Torah with even more happiness, and alongside the Festival of Weeks with even more Torah novelties: Purim. Then is celebrated the final acceptance of the Written and the Oral Law from Free Will in happiness.
And, I will give a future festival that will be almost as famous as Passover. That will stand with you as it is not even written in the Torah and alongside Yom Kippur: Tisha beAv. Its fast will be more famous. And its Prayers are not just for one more year, but about the return of the Temple forever, and the Redeemer will be born that day.
And, I will give a semi-festival that will be almost as famous as Passover. That will stand with you as it is not even written in the Torah and alongside Shabbat: Chanukah. That will have 36 holy candles that will not only light up the home but the whole world.
Everyone will feel, understand, and see that the Festivals of Tishrei are awesome but that they need the accompaniment of the other half of special days throughout the year of more hope and happiness.
Then Nissan understood that it was only elevated by Jews being extra happy for a month or two already before it, during the Month of Adar. When Jews begin learning all the Laws of Passover, 30 days before the Festival. That is exactly the day that Jerusalem celebrates Purim.