Destiny or choice ?

[Speedo]

But if the course of humanity is already written in a 2000 years old book, it mean the sum of human's choice wont effect anything at all, whatever those choice are.

When you read "The Fellowship of the Ring" (first LOTR book) and they say "blah blah we have to take the ring to blah blah and destroy it to save the world" you know that they'll manage to destroy it and the good guys will win. Why bother reading the rest of the books? Whatever happens in there won't affect anything at all, the end result is the same.