What does "as parentheses" mean?

Question

What does "as parentheses" mean in this context? Does it mean "as something added to..."?

Rituals and ceremonies are expressive occasions. As parentheses in an ordinary workday, they enclose and define special forms of symbolic behavior. What occurs on the surface is not nearly as important as the deeper meaning communicated below ground. With little time for anything not related to the task of building the machine, the Eagle Group intuitively understood the importance of symbolic activity. From the beginning, leadership encouraged ritual and ceremony.

_{Source:
Reframing Organizations: Artistry, Choice, and Leadership by Lee G. Bolman, Terrence E. Deal}

Answer 1

The ritual and ceremonies work in a similar way as parentheses work for written every-day text. Because they enclose and define special forms of symbolic behavior.

• parentheses enclose text;
• rituals and ceremonies enclose special forms.

Answer 2

From Merriam-Webster's definition of parentheses:

1 b : a remark or passage that departs from the theme of a discourse : DIGRESSION
// The speaker inserted some often amusing parentheses during his speech.
2 : INTERLUDE, INTERVAL
// The parenthesis of war interrupted the course of his life.

In short, it means that something happens outside the normal course of affairs. Both before and after this interruption, things proceed as normal.

To paraphrase the passage in question, and replace it with a specific example, you might say:

Funerals and weddings are special occasions. As interruptions to an ordinary workday, they are made up of certain rituals with defined meanings.

As an analogy, you can think of TV commercials as being parenthetical to the shows which they interrupt.