Origin of Pandora

Pandora was the first woman created by Zeus. In classical mythology, Zeus gave Pandora a box, with strict instructions that she should not open it. Pandora's curiosity soon got the better of her, and she opened the box. All the evils and miseries of the world flew out to afflict mankind. She closed the box but what she left in the box was the only good thing in the box. Hope. 

Why cant Zeus just keep it if he knows it should not be opened? Why did He gave it to her? On purpose? Was He trying to prove something or did He knew woman are very curious and intentionally gave the box to her?  When everything flew out of the box, why didn't Hope? And why was the evil created in the first place and kept inside that box together with Hope? Too many questions...