During the Three Weeks, from 17th of Tamuz to the 9th of Av, we commemorate the conquest of Jerusalem, the destruction of the Holy Temple and the dispersion of the Jewish people.
Weddings and other joyful events are not held during this period; like mourners, we do not cut our hair, and various pleasurable activities are limited or proscribed. (The particular mourning customs vary from community to community, so consult a competent halachic authority for details.)
Citing the verse (Isaiah 1:27) "Zion shall be redeemed with mishpat [Torah] and its returnees with tzedakah," the Rebbe urged that we increase in Torah study (particularly the study of the laws of the Holy Temple) and charity during this period.
Links:
The Three Weeks
There are times when love can kill. There are times when you love someone so much, you cannot allow him to breathe. He must do things the way you understand is best for him—because you cannot bear that one you love so much should be in any way distant from the truth as you know it.
“After all,” you imagine, “I must do for him what I would have done for myself!”
But true love makes room for the one you love.
True love is best expressed not in what you do and what you say, but in what you do not do, and what you do not say.