Short version. Most languages make a distinction between singular and plural “you”, but in English, they’re the same, so the KJV translators, in order to show whether it was an individual or a group being addressed, used thee/thou for individuals, and ye/you for groups.
Found that out just today and was astonished! In fifty years of reading the Bible, I’ve never guessed and never heard anyone explain it. I’ve read right over thee/thou with a certain degree of pride at how “archaic language” that some people complain about doesn’t bother me at all. It’s the same as Shakespeare and Rafael Sabatini – except that it’s NOT the same!
The people in King James’ time, along with Shakespeare and Rafael Sabatini, used thee and you according to local preference and some conventions similar to the German du and Sie (except – backwards? And let’s not dive down that rabbit hole) where it depends on the rank and relationship of the speaker to the addressee.
But in the Bible it’s totally different. God is always called “thee” but people are called “thee” too, and “you” is used, and to my now shame, it never once occurred to me to question or try to figure out why.

AI sure does take the work out of everything, even if it sometimes contradicts itself in two neighboring paragraphs, etc. At least it finds the nuggets for you, saving hours of digging.

I asked Google for examples of places where that grammar clarifies something.

So how did I eventually, after fifty years, find out about this? It was this morning, when I loaded the Bible app onto a new device, and in the course of going down the list selecting my preferred versions, I noticed and was curious about the “Y’all Version”. It is exactly as it sounds, the “Texas Receptus” in which they want to restore the distinction between you, singular, and y’all, plural. No kidding, that’s in their text. I might have read it for a while, just for the novelty, and because yes, it would be nicer to know every bit of original nuance that we can! But they added many other changes including “humans” instead of man, which would be a big distraction for me as I’m defensive about man, that is, mankind, which is MY species and I have every right to it. God created man, male and female.
I turned it off and went back to the ASV (not “new”) but I was thinking about singular and plural you and my eyes lit on the word “ye”. Is that actually a way of indicating plural?
To ask the question is to crack the mystery. Usually the problem is that we don’t ask the question.
I am rather bothered that nobody ever mentioned this to me! None of the Bible prefaces explain it, either.
If you care to know more, Wikipedia explains.
https://en.wikipedia.org/wiki/Thou
This lady has a cute way to remember which is which, in case anyone needs it –
https://micheleblake.com/thee-thou-kjv/

I haven’t read Captain Blood as many times as the Bible, but at least four XD so I kinda thought I remembered that, and AI remembers the exact quote.
AI, make me some thee and thou era scholars for my post XD