Sentence structure

These are called parenthetical commas, and they come in pairs:

Most of us spend the week telling people, or being told, what to do.

Parenthetical Commas

Place commas before and after parenthetical words or phrases:

Shakespeare’s longest play, Hamlet, is also his most popular play.

Penelope dislikes Arthur, who wears gaudy red suspenders, intensely.

My nephew, who makes Wookies out of legos, deserves a hug.

Norman, wearing his pink spandex bike shorts, stretched out thoroughly before doing his heavy squats.

Parenthetical words and phrases add extra information to a sentence without altering its basic meaning.

http://drmarkwomack.com/a-writing-handbook/punctuation/commas/parenthetical-commas/

The Parenthetical Comma

The parenthetical comma, as its name implies, is used to enclose thoughts that could be enclosed in parentheses. Such thoughts are usually interjections or interruptions to a sentence.

Examples:

• The man was, as you know, fired from his last four jobs.
• The equipment, in the meantime, sat idle and became rusty.
• We did not, however, forget that you were interested in taking over the project.

Notice that parenthetical commas can be used to enclose interruptions that are single words (such as however) and phrases (such as in the meantime).

http://editfast.com/english/grammar/commas/commas_parenthetical.htm