Human sacrifice was common in the pagan world. It was cruel but had a logic and rationale. The first child was often believed to be the offspring of a god, who had impregnated the mother in an act of droit de seigneur. In begetting the child, the god’s energy had been depleted, so to replenish this and to ensure the circulation of all the available mana, the first-born was returned to its divine parent.
Source: Karen Armstrong, A History of God, softcover edn, Vintage, 1999, p. 27.
And allow me, on that note, to pitch A Short History of Myth by same, one of the best, if shortest, books I’ve read in years. Insightful and inspiring. And short. It also comes in a beautiful mythology boxset, which is the edition I have — a present — though I haven’t read the other two books yet, so I can’t vouch for them.