Why is Miranda's virginity so important to Prospero?

Caliban, of course, had tried to Rape her. Prospero feels somewhat responsible for that. Propero, like most fathers at that time, wants to give away his daughter in a state of chaste purity.

Check this out frome GradeSaver,

Prospero seems preoccupied with Miranda's virginity because it is inextricably bound up with Prospero's own power. Her virginity is their prime bargaining chip in winning an advantageous marriage that will secure both of their positions; and if she does marry Ferdinand, their power back in Italy is secured for both of them. Virginity was often an important bargaining point‹most notably, for Queen Elizabeth, who used her eligibility to gain a great deal of power throughout her reign. If Miranda's virginity is thrown away, then Prospero's greatest hope for regaining his estate and position is gone too; so Prospero tries his best to keep Miranda well-informed of her importance, and keep Ferdinand warned as to the potential consequences of his actions. Prospero's great concern foreshadows the importance of this theme in the betrothal masque; in the masque, Iris makes mention that the couple cannot be together "till Hymen's torch be lighted," her language parallel to that in Prospero's earlier entreaty to the lovers.

yes it does bc it shows tht she is pure

its because he loved her but now he doesnt cause she is not pure. im in that situation too.