Why do the Days of Repentance immediately follow Rosh Hashanah? On Rosh Hashanah everyone does teshuvah mentally, regretting his failings and resolving to turn over a new leaf.  But this is not enough.  Teshuvah must also be done in a practical manner, through good and charitable deeds.  Many of these cannot be carried out on Yom Tov.  We can set things right during the weekdays of the Ten Days of Teshuvah. ~ Avnei Nezer