{Edited from a conversation I had about virginity.}

While chastity is often associated with virginity, the two are not morally interchangeable. In the Roman culture which disdains sex there is an ungodly idea that chastity/purity is to be without sex entirely - the ideal being perpetual virginity. Abstinence can be used for serving God without distraction (like in Paul's case), particularly in times of need, but it is not the natural design, and not what God normally desires for his followers.

Some cases where chastity and virginity diverge are of course widowhood and rape. A woman who's husband has died, or a woman who has been raped, is as chaste as any virgin, and it would be foolish and ungodly to treat them otherwise.

If a woman has been divorced by her husband, and she seeks to be married to another man while her previous husband lives, this is named defilement by the Torah; it is adultery for both her and the man she marries. If she is thus wholly defiled, even her previous husband cannot remarry her if her latter husband dies.

Another thing to consider is that God commanded Hosea to marry a harlot. If a woman commits fornication and conceals it and marries another man, she is worthy of death for this. If a woman's fornication is found out then the fornicators are to marry, but her father may disallow the marriage. Other than these considerations, another man, like Hosea, may marry one who has fornicated. A whore can of course repent, and forsake her fornication, and in such a case she can prove herself as chaste and pure from that point on as any woman.