1. In Act II Scene 4, there is further development of the sub-plot (the romance between Jessica, a Jewess, and Lorenzo, a Christian) begun in Scene 3; Jessica sends Lorenzo a missive via Launcelot that instructs him when to meet her along with other details. After Launcelot departs, Lorenzo informs his friend Gratiano about the contents of Jessica's letter in which Jessica writes that she is going to disguise herself as a page and take with her gold and jewels.
After Lorenzo tells Gratiano these details, he then reflects upon the Jew/Christian issue that also surrounds the main plot. For, Lorenzo magnifies the dislike of the Venetians (Christians) for the Jew as he says,
And never dare misfortune cross her foot
Unless she do it under this excuse
That she is issue to a faithless Jew. (2.4.35-37)
In other words, Lorenzo, pre-occupied with the "Jew-for-Jew's-sake" idea, says that if the Jew Shylock ever makes it to heaven it will be because his daughter is so good. And, if she suffers misfortune it is also because she is Jewish.
2. The atmosphere in this scene is one of secretiveness and danger as Jessica plans to disguise herself as a man, a page, or "torchbearer," as Lorenzo describes her. Also, she plans to take gold and jewels from her father's house; this is an act that will have a tremendous impact upon her father since, as Launcelot has told Jessica in the previous scene, Shylock is very stingy and excessively greedy. Clearly, Jessica's plans to steal from her father and, then, to marry a Christian--one of those loathed by Shylock--are so disrespectful to Shylock that they are sure to anger and incite her father's hatred against her.