"to him who struck down the Egyptian firstborn, for his loving kindness endures forever" (136:10). How can that be loving kindness?

Here is what the psalm does. It puts the same answer after every line, and it doesn't stop to explain the hard ones: "to him who struck down the Egyptian firstborn, for his loving kindness endures forever" (136:10), "but overthrew Pharaoh and his army in the Red Sea, for his loving kindness endures forever" (136:15), "and killed mighty kings, for his loving kindness endures forever" (136:18). What it does do is set each of these lines beside what came of it for Israel: the firstborn beside "and brought out Israel from among them" (136:11), Pharaoh's army beside "and made Israel to pass through the middle of it" (136:14), the kings beside "and gave their land as an inheritance" (136:21). And it names who these things were for: "Israel his servant" (136:22) and us (136:23-24). The chapters that tell these events take up the questions they raise, and these notes don't repeat them: Exodus 11's and Exodus 12's on the firstborn (Exodus 12:29), Exodus 14's on the hardened hearts, Numbers 21's on the peoples Israel destroyed there, and Deuteronomy 2's on Sihon. These notes apply none of it to any people today.