The difference between Rosh Hashana and Yom Kippur
There is much to say about this but we will try to provide a short answer. The month of Elul was given especially for repentance before Rosh Hashana since one is not supposed to confess his sins on the Day of Judgment. Our main goal on Rosh Hashana is to re-accept upon ourselves G-d’s Kingdom at the beginning of the new year. The very fact that we accept His Kingdom upon ourselves gives us a huge merit on the Day of Judgment. Besides this, Jewish sources say that one should privately confess his sins during the Shofar-blowing between each series that is blown. Only one’s lips should move but his words should be inaudible. The accusers do not hear this Viduy.Yom Kippur is a day of forgiveness and atonement when we completely return in repentance to G-d, and ask that He forgive us for all our sins.