Xbox CD and Shop Game?

What would happen if you buy a game online, for example, on your Xbox and then buy the same game again as a CD and then make the CD into the console? Would then transfer the game account to the CD?

Nothing is transferred to the CD. The drive is for reading only, not for describing the disc.

And what should happen? The game starts normally. But why should you buy an existing game again?

I really do not understand the question.