Final answer:
The 12-letter word denoting a group of people gathered for worship in a church or temple is 'Congregation'. This reflects a broader term, 'ecclesia', which is used in sociology to describe a nationally recognized religion intertwined with state powers.
Step-by-step explanation:
The 12-letter word for an assembly of people who worship together at a temple or church is Congregation. A congregation is a group of people gathered for religious worship. In sociology, the term ecclesia designates a recognized state religion that most members of a society belong to, which is allied closely with state and secular powers, such as the Church of England in England. In the U.S., there is no ecclesia as the country values religious freedom and separation of church and state, a foundational principle that early colonists were seeking. Churches, synagogues, and other places of worship serve as settings for these congregational gatherings.