Shakespeare uses consequences to portray the idea that sometimes the choices we make concerning love are not always wise. In fact, his theme is really more than just love. Shakespeare's theme is the consequences of all violent, uncontrolled passionate emotions, including both love and hatred.
Shakespeare especially uses Friar Laurence to portray his theme of consequences surrounding violent passion. For example, Friar Laurence points out that "[t]hese violent delights have violent ends / And in their triumph die, like fire and powder" (II.vi.9-10). In other words, Friar Laurence is saying that sudden, violent, passionate infatuation, like Romeo and Juliet are feeling for each other, often comes to a sudden end. He draws an analogy between how a fire can be quickly put out with powder, like sand or baking soda, to show that infatuation can be put out as easily as a burning fire. Not only are these lines a useful metaphor and analogy, they also directly foreshadow precisely what happens to Romeo and Juliet. Had the couple used a little more rational thought, tempered their emotions, and put off marrying until at least their relationship was made public, then they may have saved each others' lives. But it is not really their love that brings them severe consequences; it is the fact that they allow themselves to be governed by their violent, passionate emotions rather than by their rational minds, which is Shakespeare's overall message and theme.