Shiur from Rabbi Elimelech Kohn Ztl on פרשת כי תשא.  
Discussed:  

R' Chaim Shmulevitz wonders how it was possible for Klal Yisroel to rapidly fall from receiving the Torah to idol worship in the span of just a few months.  
The lesson R' Yehuda Hanasi learned from dropping his Megilah.  
Why people who go off the Derech fall much further than those that were never religious in the first place?