Why does Romeo jump over the wall to enter the Capulet's garden?

At this point in the play, Romeo and his friends Mercutio and Benvolio have attended a ball given by the Capulet family; but they wore masks so they would not be recognized, owing to the bitter feud between the Capulet's and Romeo's family, the Montagues.  However, Romeo is recognized by Juliet's cousin Tybalt, who tells Juliet's father that a Montague has invaded the ball. Juliet's father decides to be benevolent and let Romeo stay, because...

At this point in the play, Romeo and his friends Mercutio and Benvolio have attended a ball given by the Capulet family; but they wore masks so they would not be recognized, owing to the bitter feud between the Capulet's and Romeo's family, the Montagues.  However, Romeo is recognized by Juliet's cousin Tybalt, who tells Juliet's father that a Montague has invaded the ball. Juliet's father decides to be benevolent and let Romeo stay, because he behaves like a gentleman. Soon after this, Romeo sees Juliet and speaks to her briefly and falls in love with her instantly. Mercutio suggests they leave the ball, and they are bid farewell by Juliet's father.

But Romeo is smitten and feels he cannot leave. "Can I go forward, when my heart is here?" he says. He then climbs the wall and hides from Mercutio and Benvolio, who have been making fun of him for being so fickle and falling in love so soon after his relationship with Rosalind ends. Mercutio thinks he has gone to bed, but Benvolio knows he climbed the wall. They decide to leave him there to fend for himself. Romeo is annoyed that Mercurio is so belittling: "He jests at scars that never felt a wound." But Romeo then sees a light in the upper window and sees Juliet at her balcony window, and overhears her, so he decides to speak to her. 

When she asks why he climbed the wall, risking his life if he is discovered by her family, he replies "With love's light wings did I o'erperch these walls, for stony limits cannot hold love out, and what love can do, that dares love attempt. Therefore, thy kinsmen are no stop to me." With this statement he declares his love for her and his willingness to put himself in danger to see her.