After delivery, why are women not allowed to receive Holy Communion except after a definitive number of days (forty for a baby boy and eighty for a baby girl)?
This is explained in Leviticus 12:1-5. The longer period (eighty days) after the birth of a girl is a reminder of the fact that evil did enter the human race through a woman's weakness who yielded to the enemy's temptation. Humanity fell through Adam, the man. But the temptation came through Eve, the woman. "For Adam was formed first, then Eve. And Adam was not deceived, but the woman being deceived, fell into transgression. Nevertheless she will be saved in childbearing if they continue in faith, love, and holiness, with self-control" (1 Tim 2:13-15). When St. Mary gave birth to our Lord Jesus Christ, although He was sinless, untainted with the original sin of Adam that all of us carried, yet she followed and implemented Moses' laws.