Joy That's Encouraged During The Nine days

The Nit'ei Gavriel says that though it's known that we are forbidden during this time (the Nine Days, the heavy period of national mourning for Jews) from many things that increase our joy, there are things we are not forbidden to do that increase our joy.

We are not forbidden from studying and deeply experiencing Torah during these days (up until the imminent approach of the actual day of the Ninth of Av). He writes that the idea behind making a celebratory siyum (competing a significant book of Torah learning) (besides the known concept of it being a way to get around the prohibition of eating meat) is actually that we can and should increase the permitted ways of being joyful, i.e.involvement in Torah, that are allowed during these days. He tells of a prominent Rebbe who made a siyum on each one of these days, even though he did not eat meat himself, and he did so not just so others could eat meat.

By immersing ourselves more in Torah during this time we show our faith in G-d, even in sad and hard times, and reaffirm our belief that "this too is for good" (gam zu letovah). On a deeper level through this faith G-d's kindness and mercy, which is presently concealed, is elevated and becomes revealed, and brings consolation to Zion and Jerusalem.