One of the dominant prayers through the Days of Awe is Unateneh tokef: "Let us now relate the power of this day's holiness, for it is awesome and frightening." The prayer includes these awesome and frightening words:
On Rosh Hashanah will be inscribed and on Yom Kippur will be sealed how many will pass from the earth and how many will be created; who will live and who will die; who will die at his predestined time and who before his time; who by water and who by fire, who by sword, who by beast, who by famine, who by thirst, who by storm, who by plague, who by strangulation, and who by stoning. Who will rest and who will wander, who will live in harmony and who will be harried, who will enjoy tranquility and who will suffer, who will be impoverished and who will be enriched, who will be degraded and who will be exalted.
But the same tradition that provides this prayer insists that Rosh Hashanah is a solemn festival, not a somber one, a festival that requires joy.
Before leaving the House of Prayer on the night of Rosh ha-Shanah it is customary to bless one another with the benediction, “May you be inscribed and sealed for a good year.” Then it is customary to go home joyfully and to keep away from all grief and sighing, so as not to give the Accuser an opening, for the Accuser’s only place is where there is grief and sighing. One ought to trust in God, as it is written: “For the joy of the Lord is your strength.” [Seder ha-Yom, in Days of Awe, by S. Y. Agnon]
This commentary is citing Nehemiah 8, which takes place on "the first day of the seventh month." Ezra reads the Torah to the people and they weep over all their transgressions and neglect that it reveals. But the leaders say, “This day is holy to the Lord your God; do not mourn or weep. . . . Go your way, eat the fat, drink the sweet, and send portions to those for whom nothing is prepared; for this day is holy to our Lord. Do not sorrow, for the joy of the Lord is your strength.”
Of course, it's appropriate to mourn over our transgressions, but Nehemiah teaches that the holiness of the day, which derives from the holiness of the king whom the day honors, trumps even righteous mourning. It reminds me of the opening of the Book of Nehemiah, where he appears before the King of Persia with a sad and downcast countenance--clearly not acceptable behavior (Neh. 2:1-3). God is with Nehemiah through this episode, but the point remains: If it's wrong to be sad in the presence of an earthly king, how much worse in the presence of the King of all kings!
Beyond that, with great psychological insight, Nehemiah 8:10 teaches that depression and gloom will hinder us from correcting our behavior and restoring our service to the King, "for the joy of the Lord is your strength!"
There's a lesson here about moderation, too, even in the matter of repentance. Can you repent too much? Yes, if it takes the focus off of God and leaves it on you--even the sinful you. Moderation means that when we recognize our failures and sins, we turn away from them and turn back to God. We don't linger in confession and regret--although we need to practice them, for sure--but we move beyond them to return.
For His anger is but for a moment,
His favor is for life;
Weeping may endure for a night,
But joy comes in the morning. (Ps. 30:6)
Weeping and remorse are part of the Days of Awe, but a transitional part, an aspect of this age, Olam ha-zeh; joy is abiding, a glimpse of Olam ha-ba, the Age to Come. As our Messiah teaches, Happy are those who mourn, for they shall be comforted.