The author of Avodat Israel expands on this idea and compares the Almighty’s grief to the sorrow of a king, and explains the role of a king’s servants when their master is grief-stricken. “It can be compared to a king who is sometimes happy and sometimes sad. When the king is in good spirits, he doesn’t need musicians to cheer him up because he is already happy. But when he feels grief because something sad happened to him, then he needs singers and musicians to cheer him up.”
“We have to relate the same way to the Almighty,” the Avodat Israel writes. “When the Temple was destroyed, and G-d experienced sorrow, so to speak, the Almighty’s servants should make it their duty to please Him, praise His Name and make Him happy. During these days, when the King feels grief about the exile of his sons, our duty is to come to Him, deflect from His sadness and rejoice in the King’s honor. During these days of mourning, we have to say to Him, “You are our king forever, including now, and You will reign over us forever! And saviors shall ascend Mt. Zion… and the L-rd shall have the kingdom. Everyone will desire to serve You and give you the crown of kingship!”
The Avodat Israel concludes, “We should strengthen others and ourselves not to be negligent in serving G-d. Even though on Tisha B'Av we should be grief-stricken over all that happened to us on this day, nevertheless, we still have to be happy and have to gladden our King's heart about the joy that will come soon, because Messiah will be born on Tisha B'Av, may he quickly redeem us. “
In other words, we must rejoice and delight in our Creator particularly during these days when He is sad. The way to gladden our King is by serving Him in joy, observing His commandments in joy and praying for the coming redemption with anticipation and joy.
The book “Piskei Tshuvot” states that “we should diminish our happiness during these days, particularly where it concerns our own affairs. But where it concerns serving G-d, studying Torah and praying, to the contrary, we should do them with great joy and ardent desire, because it is a time to get close to the king. This is especially true of the Shabbats during the Three Weeks.” In other words, we should be happy because during these days we can get close to the king more easily.
The Maggid of Mezritch explains the verse in Lamentations in the same way: “All her pursuers overtook her between the straits” (Lamentations 1:3) — “Every Jew who pursues G-d and desires to crown our Creator over himself and the universe, will be able to achieve more during these days.” These days are truly auspicious to approach our Creator and become close to Him.
It is related that when they submitted petitions to Rabbi Mordechai Nadvorna containing the names of people who were experiencing tribulations, he would ask that the notes be brought before him during the Nine Days, because these are days favorable for all sorts of salvations.
So let us gladden our king during these days. Let us fulfill the commandments in joy, pray to Him in joy and await the coming of the redeemer together with Him.