There are different interpretations of why Hamlet tells Ophelia to go to a "nunnery" in Act III, Scene I of Shakespeare's play "Hamlet." Some possible reasons are:
He is genuinely concerned about her and wants to protect her from the corruption of the court and the male characters in the play. He sees the world as a corrupt and sinful place, and he believes that Ophelia would be better off in a place of spiritual purity and safety, such as a nunnery.
He is angry and frustrated with Ophelia for participating in the deception of his friends and family, and for betraying his trust by spying on him. He sees her as a symbol of the deceitful and manipulative nature of women, and he wants her to go away and leave him alone.