The schools of Shammai and Hillel for the very first time disagreed regarding a case of Jewish law. This occurred around the turn of the 1st century. In the ensuing generations, the schools argued regarding many different laws, until the law was established according to the teachings of the "House of Hillel" -- with the exception of a few instances. According to tradition, following the arrival of the Moshiach the law will follow the rulings of the House of Shammai.
All throughout, the members of the two schools maintained friendly relations with each other.
After a 12-day sea voyage, the previous Lubavitcher Rebbe, Rabbi Yosef Yitzchak Schneersohn (1880-1950), disembarked at the New York harbor on the 9th of Adar II of 1940, following his miraculous rescue from Nazi-occupied Warsaw.
Links:
Vintage film clip of the Rebbe's arrival in NY, March 19, 1940
More about Rabbi Yosef Yitzchak of Lubavitch
There is a place—the “fiftieth gate,” they call it—so high that all things are equally nothing from there. There is no good, no evil, nothing can be added or taken away, the righteous are dust, the wicked are dust, nothing is of consequence, all is but dust.
Drunk with the joy of Purim, a Jew travels higher and higher until he reaches that place. And there he proclaims that the oppressed have been saved; the wicked overthrown; and light, joy, happiness and peace rule throughout the universe.
“As for this high place,” he declares, “I am not impressed. It too was created for the purpose of our joy below!”
Yes, it is true that the higher you go, the less things matter. So that, for a G‑d who is called “the Infinite Light," nothing is of any consequence at all.
Indeed, nothing needs to be at all. So why does anything exist?
Because this infinite, can-do-anything God chose that it should exist.
And if all is by choice, then it is with desire, and with love, and with goodness. He chose light over darkness, good over evil, liberty over oppression, the joy of Purim over the evil machinations of a powerful megalomaniac.
He chose, and that choice became the very fabric out of which this universe was formed, the theme of every story it tells, the meaning of every life, the message of every mitzvah we do.
Its secret exposed, the fiftieth gate itself is redeemed. It, too, has served its purpose.