Yom Kippur
Yom Kippur translated a few times over means, "The day of atonement". Sounds gruesome and in many opinions, it is. The paschal lamb is raised by the family and the family becomes somewhat familiar with the lamb. Then slaughtered and eaten. (the classical biblical story)
Through the lenses of some Rabbis opinions - we, as the Chazal, are also, to a certain degree, the paschal lamb to others. In other words, the hierarchy theory of 'there is most likely someone "greater" that will complete the proverbial slaughtering of our levels of Jewish observance. For some this can seem potentially dangerous due to various events throughout the individuals / family's 'history'. However, HaShem realizes that we are also simply frail human beings, existing temporarily on Earth. So the creator of the universe, completes the 'GREAT CALCULATION' for the entire world. An extra-ordinary process and a deep mystery.
Yom Kippur consists of mostly fasting and prayer.
Having met an individual whom served in the Yom Kippur war of 1967, the military strategy and tactics of that era were very similar to, believe it or not, modern strategies. A hidden story about my 'good friend and his father' remains concealed, however, there it has been said that the Syrian General during that war was easily swayed...
The first time we ever celebrated Yom Kippur, we were alone, hidden in a room that was over 130 degrees farhrenheit.
Yom Kippur has a status of an official Jewish Yom Tov until the arrival of The Messiah. The holiday amongst the Chazal is considered to be rooted in a version, as some would say, quantum physics and various rituals and rules have been obviously modified in accordance with what is explained in the 5 books of Moshe.
Nevertheless, an extremely important Yom Tov that assists with a repentance of the previous year's, according to 'one's level', 'mistakes'.