Ever since the Golden Calf debacle, all male Israelite firstborn must redeem themselves in a pidyon haben ceremony from a descendant of Aaron, a.k.a a kohen.
Could you please explain why at a Pidyon HaBen ("Redemption of the Son") ceremony the firstborn child "costs" five silver shekels, why not ten or fifty?
In the Pidyon HaBen ceremony one finds a very strange dialogue between the father and the Kohen. "Which do you prefer," asks the Kohen, "your first born son, or the five silver shekels?"