The Chorus enters the stage and delivers a speech full of stuff you already know if you've been paying attention: Romeo has forgotten all about Rosaline and is now in love with the daughter of his enemy. Rosaline, who he once said he'd die for, didn't stand a chance when compared to Juliet.
What the Chorus adds, you probably could have guessed—namely that it's going to be hard for Romeo, a Montague, to get much quality time with Juliet, a Capulet. But...their passion makes them determined, and in time they'll find a way to meet up. Thanks, Chorus! Now we're ready to move on.