Apart from those members of the clergy who were formed within the seminary system of the Catholic Church or of a similar mainstream church, very few Independent Catholic clergy have received a formal theological education. Independent Catholic clergy "are not usually specialized professionals, but volunteers who hopefully know at least enough to celebrate the sacraments for themselves and those around them...Such radically different models of Christian priesthood raise questions of what sort of clergy training is needed, and offered within these communities." Plummer shares interviewee feedback suggesting that "the challenge of clergy training...was cited as the most important challenge facing the movement."