what's the difference between modesty and chastity?

Modesty is a social rule, therefore it can change depending on circumstances. Chastity is a Christian rule and applies to all Christians at all times, regardless of location or circumstance. So modesty is flexible, whereas chastity is rigid.

Christian chastity is different then social modesty because social modesty tells what on the body can be displayed. In regards to sex there is nothing to be ashamed of unless it is taken in excess and is done out of self-pleasure not in love. Christianity agrees with this statement because Christianity approves of the body.