Church or Sect

When I was attending a class in Sociology in Calvin College, the professor there gave the following definition of a sect: "Any group of people organized for a religious purpose which is separated from another religious group and which tends to emphasize almost exclusively the doctrinal tenet which caused the separation." The important part of this definition is the last part of it: ". . . which tends almost exclusively to emphasize the doctrinal tenet which caused the separation? When I was...