Sefirat HaOmer and Shavuot (Mitzvot 306-307)

Why do we call the holiday Shavuot? Why do Chazal refer to it as Atzeret? Why is there no specific mitzvah associated with Shavuot (aside from the Shtei HaLechem)?

The essence of Sefirat HaOmer according to the Chinuch is to express our excitement about receiving the Torah which was the purpose of the Exodus.

The two aspects of counting the Omer which can be described as לעומר and בעומר - are we counting towards an event (לעומר) or are we counting the individual days (בעומר)?

Delivered at the OU Israel Center, May 29th, 2019 (24 Iyyar 5779)