1 John 5:6
ESV - 6 This is he who came by water and blood - Jesus Christ; not by the water only but by the water and the blood. And the Spirit is the one who testifies, because the Spirit is the truth.
For follow-up discussion and general commentary on the topic. Comments are sorted chronologically.
Mary was a virgin when she had Jesus. Jesus would have had an impossibly unusual birth in that manner since her hymen would have broken as her body prepped for birth and Jesus would have been born by water and blood (amniotic fluid and hymen breaking.)
While there is blood at normal births, this is generally just the lining of the uterus sloughing off, like an extended period. Sometimes women can tear and that leads to blood as well.
But Mary has the unique position of being the only woman in history who would have had her hymen break, and thus shed virgin blood, during the labor process.
I don't believe 1 John 5:6 is telling us the details of how Mary's deliverance of the baby Jesus went down. That makes the scripture about Mary, if it is about what her body went through. That ain't what this is about. This is about the spiritual, not the physical. This is about Jesus, not Mary.
"This is He who came by water and blood --- Jesus Christ; not only by water, but by water and blood." (Both witnesses)
Jesus was born naturally. He was produced miraculously, supernaturally; but he was borne by his mother in a normal manner.
I think the verses that follow vs 6, give an explanation of what John is trying to tell us by the way he said it. He says, 'There are three who bear witness in heaven, and there are three who bear witness on earth.' He names the three for both instances; the Father, the Word and the Holy Spirit in heaven; the water, the blood and the Spirit on earth.
The water and the blood on earth are witnesses. Jesus came "by witnesses." Life witnesses!! God's testimony of life on earth is Himself, and the other two essentials for life on earth, water and blood.
Witnesses of having life in heaven: Father, Word, Holy Spirit.
Witnesses of being alive on earth: the Spirit, water, blood.
"He who believes in the Son has the witness in himself" (vs 10). There it is!! That summarized his point! (then the kicker):
John's bottom line: 'I wrote this to let you know you have eternal life.' 1 Jn 5:13
"Came by" is better understood "witnessed by..."