Ser is more of a passive verb. While, estar is more of an active verb. They mean the same thing in English, but they are very different from one another.
(30) LA ZANAHORIA (*la) comió el conejo (no la manzana) the carrot cl.acc.3sg.f eat.pst.3sg the rabbit neg the apple ‘The rabbit ate THE CARROT (not the apple).’ Given that preverbal subjects (20) and contrastive topics (22a) have similar clitic behavior, with finite enclisis...