What concept was central to the doctrines defined at the Council of Trent?

The central concept defined at the Council of Trent is faith plus good works. This council took place from 1545 to 1563 and was a key event in the Counter-Reformation, during which the Catholic Church clarified its doctrines in response to the Protestant Reformation.

At the heart of its teachings was the belief that salvation is achieved through both faith and good works, emphasizing the importance of participating in sacraments and living a moral life as part of following Christ. This marked a clear distinction from some Protestant beliefs that emphasized faith alone (sola fide) for salvation.

The other concepts mentioned do not reflect the core teachings established by the council. The idea that only clergy can interpret the Bible does not encompass the full doctrine of the Catholic Church as expressed during this period, and the notion that all interpretations of the Bible are valid contradicts the Council's assertion of the church's authority in biblical interpretation. While the council did address issues of indulgences, it ultimately reaffirmed their validity under certain conditions, rather than declaring them null and void. Thus, the emphasis on faith supplemented by good works accurately represents the council's doctrinal conclusions.