"Нечестивым же нет мира" - говорит Господь. книга пророка Исайи 48:22

Идиома. No peace and quiet for anyone; to be kept
very busy.

This term, dating from about 1900, today is used facetiously by or about a person who simply is kept very busy. It presumably echoes several biblical passages stating that God will take care of good people but will provide no peace for evildoers (Isaiah 48:22

То есть это выражение сейчас относят к тому, кто очень занят, если я правильно поняла.

Wicked это не грешник? Если по простому? Нет покоя грешникам?

Совершенно верно.

Ozzy...

Это означает, что кому-то покоя никогда нет в смысле, что он всегда занят.
-- Russ, do you ever take a day off?? Every time I come into the store, you're working!
-- What can I say. No rest for the wretched/wicked.

-- Russ, do you want to go play golf on Saturday.
-- I can't - I have to go into the office and do some paperwork.
-- On a Saturday?
-- No rest for the wicked!

i wonder why "wicked"? I could've responded - no rest for workaholics like me or something like this. Why wicked?

Because it’s from the Bible.