These terms are not so much about sex, but about a consequence of sex called babies.
You may already know that babies can sometimes occur after sex and that they most often first appear sticking head first out of a vagina. What you might not know is that when babies pass through the vagina they experience a bacterial baptism.
A traditional Christian baptism involves the sprinkling/pouring of water on your head or total submersion into the water, by a guy in a cool hat. According to the Church of England, it is a great occasion in which you get to receive the riches of his grace.
A bacterial baptism is very similar, but instead of water, you are anointed with vaginal bacteria as you leave the birth canal and there is no cool hat.
Because there's lots of evidence to suggest that babies delivered by cesarean section are at a greater risk of a number of diseases than vaginal birth babies, it's hypothesised that the bacterial baptism of vag birth promotes the establishment of a healthy early-life human microbiome.
HOWEVER, this has lead to some practising VAGINAL SEEDING, which is the smearing of vaginal bacteria on to c-section babies. This practice is NOT found to be safe or effective, calling into question the basis of the bacterial baptism hypothesis.
HOWEVER ANECDOTALLY, as someone who has received neither a Christian or a bacterial baptism, I can confirm that I am not okay.