Source: Michael Fishbane's Biblical Interpretation in Ancient Israel (New York: Oxford, 1988) 184.
"Recalling the failure of Exod. 22:28-9 to provide any written comment differentiating the treatment of human first-born from their animal counterparts (regardless of how the oral biblical tradition may have eventually harmonized this formulation with the other Pentateuchal versions)..."
Okay, I cut it off in mid-sentence.
Exodus 22:29-30 (which is actually what Fishbane means--he must use a different numbering system on a number of occasions) states the following:
"You shall not delay to make offerings from the fullness of your harvest and from the outflow of your presses. The firstborn of your sons you shall give to me.
You shall do the same with your oxen and with your sheep: seven days it shall remain with its mother; on the eighth day you shall give it to me" (NRSV).
In many cases (which I will not detail here), the Torah offers alternatives to human sacrifice, such as monetary compensation, or devoting the Levites to God as a substitute for the Israelite firstborn. But that's not in Exodus 22:29-30. Fishbane has a problem with that, for he wonders why it's absent there. Wouldn't the editor include it to avoid any impression that God wants Israelites to sacrifice their firstborn?
What intrigues me is Fishbane's reference to an oral tradition, which is a solution he proposes to his problem. If there's an oral tradition that harmonizes Exodus 22:29-30 with other versions of the law, then why did people feel compelled to write their interpretations in the text? Didn't the oral tradition take care of everything? Why write down things that people knew apart from writing?
I don't know. Why do people write anything down? Various rabbinic writings got written down so that the oral traditions could be preserved, since Christianity was attacking Judaism. Did the Bible finally get written down when Jerusalem was destroyed in 587 B.C.E.? Perhaps, but such a view would have to account somehow for the presentation of the Torah as a book in the Josiah narrative (II Kings 22-23).
Maybe there was no compulsion on anyone's part to edit Exodus 22:29-30. Scribes may have written their interpretations into the biblical texts at various points, but that doesn't mean they had to do so all of the time. People aren't always meticulous, and they make choices. As I've said before, authors are humans, not computers.
Or the scribes assumed that the laws circumscribing (or, better, eliminating) human sacrifice were clearly stated elsewhere in the Torah, so they felt no need to include them in Exodus 22:29-30.