What is the theme in A Crown of Swords by Robert Jordan?

Promises are seen throughout the story. Two of the younger Aes Sedai swear fealty to Egwene and then Egwene later has two others swear their fealty to her as well. This is noteworthy because the Aes Sedai do not swear fealty to the Amyrlin seat and because, unless they are Black Ajah, they cannot lie.