The Bible is not just a collection of teachings. It tells the story of God’s relationship with people over many generations.
Why do you think God chose to reveal Himself through real people and historical events instead of simply providing a complete set of instructions from the beginning?
we do not know All the instructions God gave Adam, nor what was passed on to the patriarchs, but we can read about how they lived, their good and bad acts and we can see they are real people, not some sort of artificial super saint.
Christianity is real because it is grounded in history by people trying to serve God.
In a practical sense I think did it that way to show them things. That there is someone behind the book. Signs and wonders things like that so that man had something in which to hope.
That’s the short version, lol.
If He just gave us a book, how would we know the author of the book? What evidence is there in a set of instructions that the instructions actually work? What proof is there that the author who claims to be a god is actually God?
The Bible is God’s revelation of Himself to mankind and is testified to by many witnesses. From the beginning, this witness of our God has been carried through the ages to us and we also have that same witness in us.
A list of instructions given by an unknown author and not verified by anyone, would have have fallen by the wayside ages ago.