The written speech level (also known as plain speech level) is often intermixed with the casual speech level in spoken Korean. It is used as a way to elevate the speaker and talk down to the listener. Often it is seen as forceful or rude when used colloquially. It is not uncommon to hear people talking to children with this speech level.
In American English:
Take a rest! means get out of my face and go shut up and stop meddling with me or this situation.
Rest! is telling someone firmly to get well if they are sick or nervous. but gently to take it easy and be okay, don't stress. You will make rverything ok for them or the situation. But is not at all near to the anger or abuse of "Take a rest" using "Take" or "Have'.