Actually, they don't KNOW this for fact.
Sure they do. They KNOW IT -- as much as I "KNOW" that Obama exists. I get that from the testimony of others.
I'm told that this funny little box in my house actually conveys "pictures" of a real person to me and that I can "see" this person "Obama" -- but I've never talked to him, I've never seen him in person -- but I've only read about him, and heard what other people have said about him. And I've read that some other people "have actually seen him".
That's another thing that I KNOW works -- is that funny little box that takes pictures from one location and carries it over to me and shows me something that I couldn't see "in person". I have only taken "other people's word" on the matter, as I've never tested out that theory to see if it works. Other people have apparently tested it out, but I haven't. BUT, I KNOW that it's true, even though I haven't tried it out.
SO ... I KNOW that Obama exists, even though I've never "tested that theory" in practice at any time in my life.
BUT, I also KNOW that George Washington existed, and I don't even have that funny little box with pictures on it to "show me" about him. In that case, I only have references from other people who assure me that those "documents" that say George Washington existed, really are true. I don't know that from having somehow tested out that idea for myself -- and I'm not quite sure how I could "test it out" by mathematics and the laws of physics right now to prove to me that George Washington existed, anyway.
However, I do KNOW that George Washington existed, because I do think the "testimony" of many others (some who saw him in person at the time and who have written about it) are true. So, I do KNOW that George Washington existed.
BUT, come to think about it -- all those things that I KNOW TO BE TRUE, in my ordinary every day life, most of it I've never tested out, I've never seen for myself and I only accept "testimony" from others that it's true.
The only thing about that, is that I've determined that most of it is "reliable testimony" -- so I KNOW that these various things are true from that reliable testimony about many things in life that I cannot directly verify.
SO..., YES ... Christians do KNOW these things to be true ... from the reliable "testimony" from God and His written word. :-)
I hope many read it.
INDEED.
THX.