Shavuos is the only Biblical festival in connection with which the Torah does not command that a Korban Chatas – sin offering, be brought.  For on Shavuos, the day on which the Torah was received, every Jew is in the category of a convert, who is considered to be “a young child who is just born.”  Just as a newborn infant is without sin, so too are the Jewish people without sin on Shavuos.” ~ R’ Levi Yitzchak of Berditchev zt”l from Torah Tavlin