So according to Famitsu's Pax interview with Yoshi-P the Astrologians stances workes by switching it between a stance to heal, and a stance to create barriers. They also apparently have a severely overpowered LB3, and the cards when drawn can be used immediatly or held back to combine with other cards for even stronger abilities.

http://www.reddit.com/r/ffxiv/commen...ast_interview/