With sincerity, fasting, and prayers-- our sins between man and G-d are forgiven by You!
All the times we forgot to bench, avoided Torah study, rushed through a shemona esrei, didn't thank You for the blessings we receive everyday, questioned Your goodness, fairness, or abilities, ignored You, stood before You in an immodest state, spurned a mitzva, and all the other myraids of things we do against You everyday... in all Your long-sufferingness and mercy you allow us a day to regret, fast, and pray and You wipe our slates clean.
Who could survive without Your mercy and kindness, Hashem?!
Thank You, thank You, thank You for Yom Kippur, Hashem!
