The story of Hermaphroditus and the story of Arachne are both obviously about a transformation.  This is an unwilling change.  Hermaphroditus merges bodies with Salmacis, and Arachne is turned into a spider.  Both have to face their fate after they challenge powers greater than themselves.  Salmacis falls in love with Hermaphroditus, but he, not knowing what love is, does not want to be with her.  He asks her to leave him alone, but when she secretly watches him she falls even harder for him.  Though Hermaphroditus did not want the nymph falling in love with him, he became a challenge to her because she could not have him.  He was so beautiful, and when he rejected her, it did nothing to stop her from trying harder.  Arachne challenged Pallas Minerva because although she was taught to weave by her, she denied it.  Later, in a more literal challenge, Minerva and Arachne compete to see who can weave a better tapestry, and as soon as Pallas Minerva sees Arachne's work, she realizes how flawless and beautiful it is.  She is so enraged that she turns Arachne into a spider.  In both stories the characters were transformed due to emotions of the higher powers, but for different reasons.  Salmacis did it because she loved Hermaphroditus; Minerva did it because she was so enraged with Arachne.  From these stories, I take the lesson not to challenge the gods because they will win.  Even though Arachne may have won fair and square, she still ended up becoming a spider in the end, and even though Salmacis originally gave Hermaphroditus a choice of what he wanted (to be with her or not), he still ended up conjoined with the nymph.