Tisha B'Av is a national mourning day, where we don't eat, drink, sleep on comfortable mattresses and we read lamentations, and are deeply saddened on that day. There are some who are not sad, but don't feel it so deeply.
Why are there people that the ninth of Av is a day of deep sorrow and others Tisha B'Av doesn't move them as much?
The difference is if we feel the loss of not having Beit HaMikdash today? Rav Bigon explains what the value of the Beit Mikdash/Temple is for us today, and as a result how we can feel mourning on Tisha B'Av - and the importance of feeling sad for lacking the Beit Mikdash/Temple.