Shavuot 5786 - "שבעה שבעת תספר־לך"

This Thursday night, we celebrate שבועות, a חג best known as being זמן מתן תורתנו. It is also one of the שלוש רגלים, one of three festivals of the year where all the men of עם ישראל were commanded to ascend to the בית המקדש to celebrate. However, when comparing שבועות to the other רגלים it seems to be alike only in the obligation of ascent. While the other רגלים each have their own unique מצוות tied to the day, the מצוות of שבועות are largely those of a standard יום טוב. But, perhaps, the most striking of all is the difference in length: פסח and סוכות are both celebrated over the course of 7 days, with both יום טוב and חול המועד, what we consider ‘standard’ for a רגל. Yet, שבועות does not follow this structure; instead, it is a one-day יום טוב with nothing to follow. But why? Why is שבועות so different from the other רגלים, and what does this tell us about the purpose of the חג as a whole?