Passover was likely an agricultural holiday pre-dating Judaism:
Nearly all ancient Canaanites — Hebrews included — were farmers, and Passover takes place just at the most critical time of the year, at the end of the growing season, just before the harvest.
This was a time of great anxiety, since the rains that made their grains grow during the winter were no longer welcome. One particularly nasty storm could decimate wheat and barley fields, knocking down the ripe plants and rotting the grains, and the people would starve.
Somehow the ancients had to stop the rains, and this could be the original function of Passover.
The question is, how could eating a roast ruminant stop the rain? For that we have to learn something about the Canaanite religion, which the Hebrews practiced before a proto-Judaism took form.
The Canaanite rain god was Baal. He is mentioned in the Bible time and again, but no details are given about the myths associated with him. To learn about these, we must consult the library found in Ugarit, an ancient Canaanite city on the Mediterranean coast of modern-day Syria.
There we find, written in a language very close to Hebrew, detailed accounts of the mythology and religion of Canaan. Among them is a story which explains why the rain stops each spring and returns every fall: the Canaanite god of death Mot kills Baal, each year anew. Baal spends his summers in the netherworld, Sheol, until being resurrected again in the fall.
“I it was who confronted mightiest Baal, I who made him a lamb like a kid in the breach of my windpipe,” Mot tells Baal’s sister Anath in the poem describing this myth.
Mot’s likening Baal’s killing to eating livestock may be key to understanding the original symbolism of Passover. Perhaps by eating a kid or lamb, the Canaanites were symbolically recreating Mot’s consumption of Baal, hoping that this would stop the rain on time.
This could explain the dictum that the bones of the Passover sacrifice must be kept intact, which the Bible does not explain. Maybe the ancient Hebrews thought that if the bones of the symbolic representation of the Baal were broken, this would adversely affect the resurrection of Baal in the fall, when rains are once again needed.
And now we have Borlaug’s dwarf wheat.
This myth may go back some 30,000 to 40,000 years to the Paleolithic Ice Age hunters in Eurasia. See, E. J. M. Witzel, “The Origins of the World’s Mythologies,” (Oxford, 2012), p. 394 and other places. Osiris is a type, but he is Neolithic.
Witzel’s broader point is that behind our modern religions there is an ancient Ice Age mythology that spans the entire Eurasian and American land masses. A related but simpler mythology spans Africa, New Guinea, Australia and related cultures. Again, the Out of Africa split.