Yeah, the two NT genealogies are kind of whack. They disagree with each other - even in the number of generations between David and Jesus. One seems to try and prove 14 generations from Abraham to David and then 14 generations from David to Jesus. Uhhhh, there's no f-n way that can work.
But it doesn't matter if Mary was descended from David - the royal/kingship descent was patrilineal, had to go through the father. And yes, had to be BIOLOGICAL father. Not step.
So if Joseph wasn't his bio-dad, wouldn't matter whether the genealogy works or not.
YEAH, and when you point it out to a Christian for the first time, it's hilarious to see their eyes glaze over.
You preface it with a couple of questions:
First, you ask if every word in the Bible is completely true, straight from God. Of course they say yes.
Then you lay the basis for their doom: "do you believe that Mary was a virgin, and Jesus was conceived immaculately?"
When you get the affirmative answer, you need to then make sure they can't weasel out:
"So Joseph was NOT the father in any biological way, right?"
They double down, firm in their belief. Of COURSE not! Everyone knows that Joseph wasn't the father!
Then the boom for the doom: "Then why does the Book of Matthew say that Jesus was descended from King David through Joseph, if he wasn't the biological father?"
At first they don't believe you - of course, THEY haven't read the damned book at all. Then you show them.
Then they go into fully mind-blown meltdown - and the basis is laid for them to ultimately question their faith. Most don't, they'll just pretend that verse isn't there. But I don't try to do this to friends that are Christians. Their happiness is built around that book, and it's tough when you realize the foundation your life is built upon is an outrageous lie. Call me a hypocrite, but I don't have the heart to do that to them.
Unless, of course, they want to force me by law to live by their beliefs, and they use the book to hurt others. Then it's Katy bar the door!