Tanya: As for the (p. 279)...the Oral Law)." (p. 279).
Shavuot is an opportune time to achieve everything in improving Torah-study and avoda marked by fear (awe) of G-d, and also to strive in teshuva concerning Torah-study, without interference by the accusing Satan - just like the time of Shofar-sounding on Rosh Hashana and the holy day of the Fast of Yom Kippur.