O gates, lift high your heads; grow higher, ancient doors. (Ps 24: 7)
The Jews presented their first-born in the Temple forty days after birth to "redeem" them, to "buy them back" from God, in memory of the slaughter of the first-born in Egypt.
God had instructed them to smear lamb’s blood on their doorframe to ward off the destroying angel. Just as the lamb was sacrificed in place of those first-born children, so too every following generation would "pay" for their own first-born, giving five silver shekels (Numbers 18:16).
