What does Juliet mean by the following lines "I have no joy in this contract tonight. / it is too rash, too unadvised, too sudden; / too like the lightning, which doth cease to be / ere one can say it lightens

Well, don’t swear. Although you bring me joy, I can’t take joy in this exchange of promises tonight. It’s too crazy. We haven’t done enough thinking. It’s too sudden. It’s too much like lightning, which flashes and then disappears before you can say, "it’s lightning." My sweet, good night. Our love, which right now is like a flower bud in the summer air, may turn out to be a beautiful flower by the next time we meet. I hope you enjoy the same sweet peace and rest I feel in my heart.