Ki Savo

.תַּחַת, אֲשֶׁר לֹא-עָבַדְתָּ אֶת-יְהוָה אֱלֹהֶיךָ, בְּשִׂמְחָה, וּבְטוּב לֵבָב--מֵרֹב, כֹּל

The literal translation of the posuk suggests that the Tochacha comes as a punishment for not serving Hashem with love and joy. The meforshim ask, why is the punishment for not being bsimcha so harsh, deserving of all 98 curses?
R' Yitzchok Hutner Zatzal explains. We are bound to serve hashem. We can do it out of our love for him- with joy. Or we will be forced to do his will- through the tochacha.
If one has weak eyesight there are two ways he can cure and strengthen it. He can cure it naturally, by exercising and strengthening his eyesight on his own until his sight is back to it's natural level. Or he can have surgery to cure him. The second option offers an effortless cure. All he has to do is sleep through the surgery and wait a few days or weeks to recover and his sight will as good as new. This sounds like the easier and better option, but it is fraught with danger and pain. There will be days that he will be bandaged and not be able to see anything. And there will be days that will be filled with pain. After all the difficulties he will have healthy eyes. The first option might be harder work, but is safer and pain free.
Klal Yisroel in galous is blinded. Hashem and his glory are hidden from us. The Kotzker once said "Where can you find Hashem? Where ever you let him in." We have to lift the darkness off our eyes and let Hashem into our lives. We can do it on our own through hard work. Every mitzva we do, every bit of avodas hashem we do, we come closer to Hashem. It's hard work but if we try and start, we are guaranteed to succeed. The other option is for Hashem to 'surgically' remove us from the darkness by shining his great light onto the world. If we choose this option we have to realize that the darkness will get darker and more painful before we are cleansed from the darkness. Only after the birth pangs of moshiach will we be redeemed.
We could, and should, serve Hashem on our own because we want to, with joy- bsimcha uvtov levov. If we refuse to do the hard work the only way we will leave this galous is through the tochacha. It will not be as a punishment, but as the last resort to save us and bring us home to our loving father Hashem.