You asked why try, if God already knows all who are his? Because we don't know. That's why.
I said why try becuase if you are already chosen, fate, God's fate, will intercede at some point in your life regardless of whether you try or not.
Okay, but that's not what skeptics here and elsewhere have said. They've said that the Bible can't be taken seriously because there is no town of Nazareth, no king David, no Hittites, no Belshazzar, etc., only to be proved wrong by new Archaeological discoveries.
no Hittites? No king David?
The problem is Archeology will always be incomplete. Do we even know king David's name was King David? Is there any surviving record of his existence? We will never know. However, it's very likely he did exists becuase as you pointed, many other things, locations and people have been verified by outside sources. So it seem like a poor argument to me.
Now, that leaves some of the details in question...but that's another discussion
