Final answer:
A cult is typically the least stable form of religious organization because it is small, secretive, and exerts high control over its members with a charismatic leader, while sects can grow into denominations and have more stability and influence on society.
Step-by-step explanation:
The least stable form of religious organization is typically a cult. This term refers to religious groups that are small, secretive, and often highly controlling of members with a charismatic leader. In contrast to a sect, which can be a small and relatively new group that sometimes breaks away to return to fundamental beliefs or practices, a cult is generally considered the least stable and influential on society.
Sects, on the other hand, may start off small and new, but they hold the potential to grow into larger denominations. Most of the well-known Christian denominations in the United States, such as Methodists and Baptists, began as sects. Some sects that do not grow into denominations, like the Amish or Jehovah's Witnesses, are known as established sects with a mix of sect-like and denomination-like characteristics.
Denominations and ecclesia are forms of religious organizations that are larger and more integrated into society. Denominations like the Methodist and Seventh-day Adventist are mainstream religions that are not sponsored by the state, while ecclesia represent an even more established church that may have a formal state relationship.