All of Sefer Bereshit, in four chapters, for Chag Shavuot:
Toledot HaShamayim v'HaAretz
Avraham
Yitzchak and Yaakov
Yisrael
The first two have been mentioned before. The third and fourth have less dramatic changes, but still there are changes. The third chapter is until the final separation from Edom, the fourth is about Yisrael only, until the end of Sefer Bereshit.
On Shavuot, we think about Ruth. I think about Tuv too. May the above links be helpful.
Chag Sameach!
