After hearing about the brawl of Act I scene 1 and then also telling Benvolio about what is really troubling him, Benvolio and Romeo hear about the ball that the Capulet household is holding that night. Benvolio, desperate to find any way he can to distract Romeo from his love-sick attitude and his depression, suggests that they go together to this ball to enjoy themselves and have some diversion, and also so that Benvolio can show Romeo women who are much more beautiful than Rosaline. Note what Benvolio says to Romeo:
At this same ancient feast of Capulet's
Sups the fair Rosaline whom thou so loves;
With all the admired beauties of Verona.
Go thither, and with unattainted eye
Compare her face with some that I shall show,
And wi will make thee think thy swan a crow.
Benvolio thus hopes to make Romeo see how ridiculous he is being for being so mournful for love of Rosaline when there are so many more deserving women out there.