As Mercutio describes Queen Mab, he associates her with dreams and fantasies, stating that she "gallops night by night / Through lovers' brains." This imagery suggests that love exists mainly in the realm of imagination and not in reality, showing how love is often fueled solely by desire and not driven by logic.
He speaks of her as a capricious, impulsive, and fickle ruler, often changing her mind as quickly as "in a dream," further emphasizing the unpredictable and uncontrollable nature of love. The passage also makes humorous allusions to the physical aspects of love, implying that love can be intoxicating, obsessive and even painful, like the "dagger of lath" she uses to prick lovers' thumbs
Mercutio warns Romeo against the power and illusions of love, showing how it can consume people and make them act in irrational and impulsive ways. However, it can also be interpreted as his commentary on the irrationality of love in general, expressing his feelings that love is essentially driven by desire and fancy, and not by reason.