What is the effect of Laertes's talk with Ophelia in scene 3?

In Act I Scene III of Hamlet, Laertes is about to depart for Paris, where he will return to his studies. Before he leaves, he gives some brotherly advice to Ophelia concerning her relationship with Hamlet. In no uncertain terms he advises her to break things off with him. According to Laertes, Hamlet is simply using her; whatever he might say, he doesn't really have true feelings for her. He is merely flirting with Ophelia. As with so many other hot-blooded young men, Hamlet's simply going through a phase; it won't last. And besides, he's of a higher social class than Ophelia, so she shouldn't harbor any serious thoughts about spending her life with him.
Ophelia is as dutiful a sister to Laertes as she is a daughter to Polonius. Yet it's almost certain that she's terribly upset at their advice to stay away from Hamlet. Her heart tells her that Hamlet's declarations of love are true and that they really do have a future together. Though outwardly, Ophelia will remain obedient to her father and brother, inside she cannot help having deep feelings for Hamlet. This is a real danger for Ophelia, for if Hamlet should one day reject her, then she would have nowhere else to turn, and would be even more upset than she is at the end of Laertes's lecture.