wants to Juliet to get married quickly because he believes this will help cure her grief. He has watched her crying and crying inconsolably and thinks this is due to her cousin Tybalt's death. He has no idea she is pining for Romeo.
Lord Capulet also fears that if she does not calm down soon, the grief, which he likens to a violent storm at sea, will damage or destroy her body, as a violent storm does a ship. He says,
Without a sudden calm [grief] will overset
Thy tempest-tossèd body.
Lord Capulet is convinced that a quick marriage will settle her down and take her mind off her sorrows.
Lord Capulet is emotionally on edge. He has worked hard to pull off this marriage and expects Juliet to be thrilled. He loses his temper when she refuses the wedding to Paris. His wife encourages him to calm down, saying he is too angry:
You are too hot.
Lord Capulet agrees that he is "mad," saying he has worked tirelessly to secure a good marriage for his only daughter. He feels he has delivered everything she could possibly want in Paris, who is good-looking, wealthy, well connected, and eager to marry her. He blows up because, from his point of view, Juliet is acting like a spoiled child.
The scene is filled with dramatic irony. We as an audience know that Juliet is not spoiled, but desperate to avoid a marriage with Paris when she is already married to Romeo.