What do Jessicca and Lorenzo think of Portia?Why is there opinion important enough for Shakespaere to show?

They think she's the perfect wife and hostess.

Sorry, I need to address the second part of your question. As to the way in which Portia is regarded, it is important to note that her actions were not the normal, accepted behaviors of a woman at the time. The opinion of those closest to Portia helps us to understand the respect she is given as a person and gives the audience a better glimpse of her as well.