The highlight and pinnacle of Jewish history was Har Sinai, meeting Hashem at the mountain. We were exalted and lifted to zenith heights. I heard from Rav Yitzchok Fingerer shlita, that perhaps this would affect our egos. Hashem bids us to remember our beginning as slaves. Perhaps this is why the Torah reading on the second day of Shavuos references both Har Sinai and the fact that we were slaves. This is alluded to in the pasuk “Vayichan Shum Yisrael neged Hahar” (Shemos 19:2) the word Hahar is gematria 210 to remind us of our 210 years of slavery in Mitzrayim.
