The whole year is about an individual's struggle against his internal forces of evil as he tries to become a perfect person. Tish'a b'av is the same thing on a national level. It's about our national struggle against evil as we try to rectify the wrongs we have done so that Hashem will see us worthy of revealing Himself to the world and making it perfect.
Put slightly differently, the whole year is about us trying to reach shleimus for ourselves, Tish'a b'av is about HKB''H bringing the world to shleimus. He wants to show Himself and bring the world to shleimus but He knows that doing that would remove our bechira so He has taken a step back and allowed us to work on ourselves at our own pace. Hashem is in golus, so-to-speak, He is in pain, waiting to show Himself but He doesn't want to do it until we've finished our mission, so that we can be zoche to olam haboh. He is being utterly selfless in this way, unbelievably patient, watching us take our time in our avodah, the avodah that needs to be done for both us and the world to come to shleimus.
It's so easy to be entirely self-focused, thinking only about our own struggle with the yetzer horah. It's easy to believe that we will make it in the end, we will be tazidikim before our end, we will certainly say vidduy and do teshuvah and we'll be zoche to olam haboh. And of course that's good, it's what Hashem wants, but what about Hashem Himself? He's waiting to reveal Himself to the world and end all our suffering but He wants to wait for His children to get what they need first.
That's what Tish'a b'av is about. It's about the golus of the shechinah and how much suffering that has brought to the world and how much Hashem wants it to end, but He is waiting for us. Therefore, we as a nation must do teshuvah and enable that to happen. And we as a nation do teshuvah by each individual doing teshuvah. If we all take responsibility for our own teshuvah then iy''H we will be successful, and others will see our successful teshuvah and be inspired to do the same. That's all we can do.
Seforim speak about the aveiroh of being motzi shichvas zerah levatoloh and say, among other things, it causes the giluy shecinah to be delayed. This is one of the main things that is getting in the way of us completing our national job thereby allowing Hashem to reveal Himself to the world. So in a way I feel that Tish'a b'av is a reminder of how much we need to work in this area. It's not just for ourselves, it's for Hashem and for the good of klal yisroel and the world.
Fast well, chevra, and stay out of the heat tomorrow.