Now I write these things unto you, not that I know there are any such persons among you; nay, indeed I hope that God will never permit any such report to reach my ears, He "who spared not His Son for the sake of His holy Church." But foreseeing the snares of the wicked one, I arm you beforehand by my admonitions, as my beloved and faithful children in Christ, furnishing you with the means of protection against the deadly disease of unruly men, by which do ye flee from the disease [referred to] by the good-will of Christ our Lord. Do ye therefore, clothing yourselves with meekness, become the imitators of His sufferings, and of His love, wherewith He loved us when He gave Himself a ransom for us, that He might cleanse us by His blood from our old ungodliness, and bestow life on us when we were almost on the point of perishing through the depravity that was in us. Let no one of you, therefore, cherish any grudge against his neighbour. For says our Lord, "Forgive, and it shall be forgiven unto you." Give no occasion to the Gentiles, lest "by means of a few foolish men the word and doctrine [of Christ.] be blasphemed." For says the prophet, as in the person of God, "Woe to him by whom my name is blasphemed among the Gentiles."
But as to servants, what can we say more than that the servant should bring a good will to his master, with the fear of God, although his master be impious and wicked, but yet not yield any compliance as to his worship? And let the master love his servant, although he is his supervisor. Let him reflect on the fact that each shares equally in the other’s humanity. And let one who has a believing master love him both as his master, and as of the same faith, and as a father, but still with the preservation of his authority as his master…. In like manner, let a master who has a believing servant love him as a son or as a brother, on account of their communion in the faith, but still preserving the difference of a servant.
Let them count them "worthy of all honor," he says; for do not suppose, because you are a believer, that you are therefore a free man: since your freedom is to serve the more faithfully. For if the unbeliever sees slaves conducting themselves insolently on account of their faith, he will blaspheme, as if the Doctrine produced insubordination. But when he sees them obedient, he will be more inclined to believe, and will the rather attend to our words. But God, and the Gospel we preach, will be blasphemed, if they are disobedient. But what if their own master be an unbeliever? Even in that case they ought to submit, for God's Name's sake.
Those who have believing masters must not be disrespectful on the ground that they are brothers. Rather they must serve all the better since those who benefit by their service are believers and beloved. In the epistles to the Ephesians and Colossians he commands the same. So it is obvious that Paul’s intention is not to abolish slavery as a social institution. Rather, he attacks slavery in its worst form, the slavery to evil, which pays no respect to any external freedom.
[AD 108] Ignatius of Antioch on 1 Timothy 6:1