'Watchman' in the Bible

Son of man, I have appointed thee a watchman unto the house of Israel, and thou shalt hear the word from my mouth, and give them warning from me.

Son of man, speak to the children of thy people, and say unto them, When I bring the sword upon a land, and the people of the land take one man from among them all, and set him for their watchman:

But if the watchman see the sword coming, and blow not the trumpet, and the people be not warned, if the sword come and take a person from among them, he is taken away in his iniquity; but his blood will I require at the watchman's hand.

So thou, son of man, I have set thee a watchman unto the house of Israel; and thou shalt hear the word from my mouth, and warn them from me.