"Fiduciary duty" is a legal term of art: in practice, it means that certain people in positions of trust have a legal duty to put another's interests ahead of their own interests (not unlike the typical theological definition offered for "agape" love mandated in the New Testament). Trustees, certain business associates, lawyers and doctors are among the most common categories of people held to this standard. Smith's ruling also is expected to open another legal channel for attorneys to bring civil suits against churches for clergy abuse cases, according to Lisa Bruno, news editor for Massachusetts Lawyers Weekly. Given the overlap between the definition of a "fiduciary duty" and the New Testament commandment for the church, there should not be much tension here.
It was easy to see this coming, I think; there has been a growing frustration about the fact that there seems to be insufficient legal incentives for religious groups to prevent serious clergy abuse. People tend to be more trusting of relgious groups and clergy, leaving themselves vulnerable to exploitation where there are niadequate institutional safeguards or screening of those in leadership positions. Such trust and concomitant vulnerability seems to be the underlying essence of a legal fiduciary. In addition, institutions are often the best insurers against these types of risks: they can purchase liability insurance organizationally (obtaining economies of scale), and they have private or internal information about potential loci of abuse (information not readily available to outsiders). The information asymmetry puts the religious organization in the best position to identify potential hazards and prevent the harms before they occur. I understand that the ruling is unfavorable to churches in the immediate sense, but in the long run, denying that there is a fiduciary duty to members - that members can "trust" the church in a special way - undermines the credibility of any religious or spiritual institution.