Bereishit is a cheerful parsha, even though its ending is not all that pleasant.
Parshat Noach has the Flood, but the week ends on a happy note with the birth of our father Avraham.
The really joyous week is that of parshat Lech Lecha. We live every day of the week with Avraham, the first to dedicate his very life to spreading G-dliness in the world.
Avraham bequeathed his self-sacrifice as an inheritance to all Jews
--From Hayom Yom