Shylock asks Jessica to shut the doors so as to protect his peaceful home from the sounds of "shallow foppery".A masque was organised and he did not want the sounds of drums and wry-neck'd fife to enter his house.He even asks Jessica not to clamber upto the casements and thrust her head into the public street to watch the Christian fools with varnished face.
Because shylock doesn't like the christians.he hates them be cause bassanio had borrowed some money  from he says her not to put her head out of the windows and look at them and to shut the doors