I never looked at the story as addressing that, and there's still LOTS of reasons for it. Mostly, it's one of the plagues God sent on Egypt. That's a level of understanding we can get from a "surface reading." This is really important to the Jews, who consider this their most important book.
That's part of why we have the term "Judeo-Christian heritage." The Passover (Israel's firstborn not being killed along with the Egyptian's) is clearly a foreshadow of our Highest Holy day: Easter!
So in conjunction with what Jason shared with us this story also affirms we need to kill off God's enemies
within us in order to be born again. This is something Scripture tells us over and over, as our understanding grows deeper. It's also part of the experience of every born again believer; in one way or another we all turn from our own known sin before Jesus comes in to make His abode with us.
So we see we do not at all need the OT stories to know what we're
supposed to do; it's just that with better understanding we gain a much stronger purpose for doing what we know.
And God is good