'O God' in the Bible

He shall not make himself unclean for his father, or for his mother, for his brother, or for his sister, when they die; because his separation unto God is upon his head.

And Moses cried unto Jehovah, saying, Heal her, O God, I beseech thee.

And they fell upon their faces, and said, O God, the God of the spirits of all flesh, shall one man sin, and wilt thou be wroth with all the congregation?

And Balaam said unto God, Balak the son of Zippor, king of Moab, hath sent unto me,'saying ,