Capulet is very typical of the "middle ages" kind of father. Juliet is 14 and certainly old enough to be married. He wants to be sure that she is married to a "friend of the family" and one whose station is secure.

Paris is the man that meets the conditions. Mr. Capulet arranges the marriage for a Thursday because it is already Monday and too soon after Tybalt's death to have a wedding party.

Monday! ha, ha! Well, Wednesday is too soon,
O' Thursday let it be: o' Thursday, tell her,
She shall be married to this noble earl.

He wants his wife to convince Juliet of the arrangement, but he will force Juliet to marry Paris if need be.

Well get you gone: o' Thursday be it, then.
Go you to Juliet ere you go to bed,
Prepare her, wife, against this wedding-day.

No one knows that Juliet is already secretly married to Romeo.