I'll never forget reading this passage for the first time. We've been socialized enough in the United States to believe God loves us, and in fact probably think he's more pleased with us than He really may be!
But because Egypt is so prominently against Israel, Moses and Assyria is used as the hammer for smashing Israel and Judah, I don't find myself imagining God calling them his people, his handiwork.
But there it is in the prophet Isaiah. I challenge you to read Isaiah 13-24 and think about who is speaking and who is the audience. One of the best and most helpful things I can teach you about reading the prophets is this:
1. Who is speaking?
God? Isaiah? A king? A nation or God quoting a national voice?
2. Who are the hearers of the speaking?
Is it the prophet listening? Is God speaking directly to the nation? Is it to Samaria or Israel to the North? Is it to Judah in the South? Who is the audience?
3. What other writings can give you background, specifically within the Bible itself?
For Isaiah, for example, the background is giving in 2 Kings 16-25 about how Isaiah prophesied to four kings, and more detail about these kings is given. You can also read in 2 Chronicles 26-32. You can also find helpful background in other prophets contemporary with Isaiah. The prophets contemporary to Isaiah, even if some of them worked in Israel to the North, are Micah, Amos, and Hosea.
4. What are the themes and metaphors being used?
We can't always know for sure who certain symbols and references point to, but many can be discerned by careful reading with a study Bible and reading in context. In other words, reading whole chapters and chapter to chapter seeing the connections from one thing to the next.