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
Perhaps a person will say,
“I cannot fathom an infinite Creator, so why should I attempt to do so?”
“And why should I attempt to awaken my heart to show Him love? What can the love of this puny creature provide Him?”
“So I will just serve Him in complete surrender, doing that which is to be done, connecting to a will and desire far beyond my own.”
Such a person may be wise, but he is wrong.
Yes, it is absurd, but G‑d desires to be grasped by your human mind.
Yes, it is inconceivable, but He desires to find a home within the innermost chamber of your heart, no matter how tiny that place may be.
For this He created you, so that He could dwell within your world.
Serve G‑d with all your heart and all your mind—because that too is His unfathomable, unbounded desire.