Wow. You stumped me.
Thanks to the magic of Google, I found this sermon from a Conservative rabbi that asks that very question:http://netivottest.org/5769-bo-buchinAs is typical in Judaism, the sermon focuses more on the questions than on the answers. That said, there's an interesting argument that the dominant Egyptian god had a ram's head, so a bunch of Israelites slaves slaughtering sheep and painting the blood on their doors would have taken a lot of chutzpah and been seen as a huge insult to the local god. That would have made painting the blood an act of faith - because no one is going to risk pissing off the local slavemasters if they aren't confident that someone/something has their back.
So a bunch of lambs had to die so that some random god would be insulted? That's... barbaric.
In this theory, it would be the Egytians who would be insulted - and it would be a sign that the Israelites were no longer afraid of them.Tosafot (ancient Jewish commentators) also suggested that taking the lambs would have attracted the interest of the Egyptian firstborns, who subsequently pleaded with Pharoah to release the Israelites and then rebelled against their own families.It's a good question. I'm not expecting you to accept the answers. It's just an illustration of how we tend to find that scholars have wrestled with similar questions throughout the ages, and how a different interpretation can put a different spin on a question.
I still think the Egyptians were only insulted for their deity. The act itself doesn't insult Egyptians so much as a god in their religion... but I suppose that's semantics.
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