Into the fold

What is the meaning & origin of "into the fold"? as in welcome into the fold, or come into the fold.
Thank you. Paul Dean

The dictionary (in this case, dictionary. com) defines "fold" as
fold2 n.
A fenced enclosure for domestic animals, especially sheep.
A flock of sheep.
A group of people or institutions bound together by common beliefs and aims: "He is a living testament to the wisdom of admitting lay psychoanalysts into the official fold" (Jerome Bruner).
A religious congregation: The priest welcomed new parishioners into the fold.

Many religions (and other organizations) demand sheep-like obedience from members. It promotes coherence, and assures the control of the shepherds.