Tisha B’Av and the missing mitzvos is something central to every Jew. On the 9th of Av the holy Beis Hamikdosh was destroyed which led to exile. This resulted in many mitzvos no longer able to be fulfilled. In fact, from the 613 positive and negative commandments, only 271 mitzvos can be done nowadays. That means the majority, 342 mitzvos, currently cannot be done! This is part of our great aveiles and sadness specifically on Tisha B’Av, as well as throughout the year, that our spiritual lives have been minimised, further distancing us from Hashem. What we must do is strengthen ourselves in the mitzvos that remain with us and feel the loss of those we currently cannot do that will come back with the coming of Moshiach, may he speedily come now.