The Jewish people had sinned, and their future stood in the balance. G-d's initial plans to destroy the people were thwarted by the intense prayers of Moshe, and it was on Yom Kippur that our covenant with G-d was reestablished. And on the very next day, the construction of the Mishkan began.
"G-d wanted to give merit to the Jewish people; therefore, He increased for them Torah and mitzvoth". A Jewish way of life offers so many opportunities for mitzvoth. We accumulate mitzvoth--and hence, merit--for such things as saying good morning to a passerby, conducting a business transaction honestly, showing up in shul to hear shofar, eating a meal on Shabbat, and many other activities that are both easy and enjoyable.