'Master' in the Bible

Therefore I warn you, and I implore you in the name of the Master, no longer to live as the Gentiles in their perverseness live,

And, ye masters, do the same things unto them, forbearing threatening: knowing that your Master also is in heaven; neither is there respect of persons with him.

For our struggle is not against flesh and blood [contending only with physical opponents], but against the rulers, against the powers, against the world forces of this [present] darkness, against the spiritual forces of wickedness in the heavenly (supernatural) places.