For the first several verses, the refrain follows naturally after each phrase. We give thanks to God because of who he is (v. 1-3), then because of his awesome work of creation (v. 4-9). In both these things, we can know and trust that God's steadfast love endures forever.
However, we then get into the exodus and settling in Canaan. Verse 10a may be jarring to us: "to him who struck down the firstborn of Egypt." This is followed again by the refrain "for his steadfast love endures forever." How are death and the plagues on Egypt connected to his steadfast love? One may experience a similar dissonance with verses 17-20, speaking of the destruction of kings and their people in settling Israel in the land of Canaan. Again, how does this connect to God's steadfast love that endures forever?
Let me point you to Romans 9. Go read it and come back.
As we see here, God will have mercy on whom he chooses. He has set his love on his people. These are the people who he called to himself, to whom he gave his law, and who he redeemed out of Egypt. It is also who he has called out of darkness to light, out of sin and guilt to be free of our sins, who he has clothed in righteousness not our own. It is the people that Jesus suffered and died for, taking on our penalty.
This love is not for the world. All people are justly condemned for their sin. We all deserve death of body and soul, including pharaoh and all the firstborn of Egypt, and the kings of Canaan, and you and me.
But, God's love is indeed for those who trust in Christ's work alone to be saved from our sins. We are forgiven. And, our God will fight for his people against this remaining wickedness in the world, whether in Egypt, Canaan, or Sylva, NC, on behalf of his people.
And that is indeed a love that is steadfast, and endures forever.
