The Shabbat after Tisha B'Av is called Shabbat Nachamu, after the haftara that is read: "Nachamu, nachamu ami" (Be comforted, be comforted my people). Why is the word nachamu repeated? To offer consolation for both Temples, which were destroyed.
The word nachamu means comfort. God is saying: with all the hardships you and the rest of the world have gone through, you can still find the deepest of comfort inside yourself. Have you ever felt so sad that you thought you would never stop being sad? Did your dog die or did your best friend move away? But you didn't remain sad forever. You moved on -- you got a new dog; you visit your best friend in the summer. You learned that there was a deep part of you that could heal the pain.
Remember that next time you have lost something very close to you and you feel like you will never be whole again. The feeling won't last. You will "be comforted" and you will be happy again.