The ten days between Rosh HaShanah and Yom Kippur are called "Aseret Yamim HaNorayim", usually translated as "The Ten Days of Awe", referring to the awe inspired by G-d that culminates in the closing of the Book of Life at the end of Yom Kippur. It implies that during nthose ten days we stand in Awe before the Lord awaiting the Divine Judgement.
Why only 10 days? Archeologists will tell you that the number 10 is mystical (along with 3 and 7), and that it also relates to some pre-Hebraic Canaanite customs. I say, whatever the origin, it is a reminder that our destiny is ours to make or destroy through our actions, and that ultimately there is a higher power.
So again, why only 10 days? The evidence of that Higher Power is in front of us every day of our lives... in the bee that polinates the flower, in the rain that feeds the land, in the smile of those we love, and in so many other things we sometimes take for granted - like Health, Freedom, Love...
If we stand in Awe for only those 10 days, it is kind of egoist, because we are doing it to ensure a good Judgement. I propose that we should be standing in Awe of the Higher Power every day of our lives. Every day is an opportunity to recite the "She'Echeyanu".
So what about "Aseret Yamim Ha'Norayim"? The Hebrew phrase can be more properly translated as "The Ten Terrible Days". They are terrible in the sense that they are ten days in which we stand in expectation of the Judgement and we wonder if our behavior has been the right one. They are ten days of self-questioning and self-doubt. They are ten days to acknowledge our mistakes and make ammends. They are not Ten Days of contemplation; they are Ten Days of Action, in which we must prove that we learned of whichever mistakes we have made. They are Ten Days of Growth, but also Ten Days of Doubt, during which we accept we are not infalible, but only Human. Far more difficult than just "standing in Awe", but then - as the Yiddish saying and Mel Brooks say - "It is though to be a Jew" ("It is schver tzu zain an Yid").
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