The idiom into the fold means to welcome to part of a group of people who share the same faith or system of beliefs.

What does the slang term fold mean?

Definition: Drunk. Type: Slang Word (Jargon)

What does it mean to leave the fold?

When someone joins an organization or group, you can say that they have come into the fold. When they leave the organization or group, you can say that they leave the fold.