Rosh Hashanah, the Jewish new year, is traditionally a day for wishing people well in the year ahead. Yom Kippur greetings, by contrast, are more solemn, as befits this day of atonement. Each day has its own traditional sayings.
https://www.learnreligions.com/rosh-hashanah-and-yom-kippur-greetings-2076426

