Shavuos Versus Simchas Torah

What is the difference between Shavuos and Simchas Torah if they are both fundamentally celebrations of the Torah?

Answer

Another angle, given in various places in Chassidus, and developed further in one of the Lubavitcher Rebbe's talks (Likkutei Sichos, vol. 14, pp. 156ff - English adaptation on chabad.org) is that Simchas Torah specifically commemorates the giving of the second Tablets on Yom Kippur, and so we celebrate it at the end of that season of holidays.

In this talk, too, the Rebbe points out two other related differences:

1. 
   

   Shavuos commemorates how G-d gave us the Torah (as an "arousal from above"), while Simchas Torah focuses more on our own efforts in Torah study (an "arousal from below"). (This of course also relates to the idea that Yahu mentioned in his answer, and in particular, to item 3.)

   
   
   


2. 
   

   At the original Giving of the Torah on Shavuos, we were tzaddikim. By contrast, on Simchas Torah we celebrate how we became baalei teshuvah.