Answer:
Has feathers but can't fly. Rests on legs but can't walk.
This is needed both for courage and hardcover books.
There is an ancient invention. Still used in some parts of the world today. That allows people to see through walls.
I build up castles. I tear down mountains. I make some men blind. I help others to see.
You can read it both ways, I wearΝΎ One way it's a number, reversed a snare.
What do you purposefully put lots of in and on your body, but run away from when you encounter it outside?