ANSWER

The main point in שירת האזינו is that _______________ that happens in this world comes from Hashem, even those things that seem to be the opposite of good.
And, more importantly, that He is doing all of it for one purpose, and that is the true and complete ________, when we will see and understand the truth behind it all.
This is why even though שירת האזינו includes some harsh words, it is still a שירה, since it all ultimately brings us to the גאולה.