Answer:
Open me, and you can't see me without a mirror. Close me and you can't see me at all. What am I?
I spend the day at the window go to the table for meals and hide at night.
When I live I cry if you don't kill me I'll die.
In wealth I abound; in water I stand; as a fencer I'm valued all over the land; at Venice I'm famous; by farmers I'm prized; respected by law yet huntsmen despised; consternation and ruin ensue when I break; And the beasts of the forest advantage won't take.
I may only be given but never bought. Sinners seek me but saints do not. (one word).
What do you purposefully put lots of in and on your body, but run away from when you encounter it outside?