1 Corinthians 7:23

"Ye were bought with a price: become not bondservants of men." This saying is addressed not to slaves only but also to free men. For it is possible for one who is a slave not to be a slave; and for one who is a freeman to be a slave. "And how can one be a slave and not a slave?" When he doeth all for God: when he feigns nothing, and doeth nothing out of eye-service towards men: that is how one that is a slave to men can be free. Or again, how doth one that is free become a slave? When he serves men in any evil service, either for gluttony or desire of wealth or for office' sake. For such an one, though he be free, is more of a slave than any man. But if this be not the meaning, if he bade them forsake their masters and strive contentiously to become free, in what sense did he exhort them, saying, "Let each one remain in the calling in which he is called?" And in another place, "As many servants as are under the yoke, let them count their own masters worthy of all honor; and those that have believing masters, let them not despise them, because they are brethren who partake of the benefit." And writing to the Ephesians also and to the Colossians, he ordains and exacts the same rules. Whence it is plain that it is not this slavery which he annuls, but that which caused as it is by vice befalls free men also: and this is the worst kind of slavery, though he be a free man who is in bondage to it.