In Paul's churches there were two categories of slave. The first had come to Christ independent of their masters. From what we have seen of their mobility, this is not at all surprising. But normally the religion of the master determined the religion of the whole household. Any deviation in this pattern would probably not escape notice.
Apparently certain Christian slaves were taking home with them some rather radical ideas. Instead of finding contentment in the hope that God would reward their humble diligence (Eph 6:5-8; Col 3:22-24; compare 1 Pet 2:18-20), they began to treat their masters with disrespect. The masters could not help but think that this insubordination had something to do with the new religion and the one called Christ. What possible good could come from a religion that encouraged such revolutionary behavior? The insubordinate behavior of slaves posed a definite threat to the church's reputation.
Consequently, Paul issues corrective instructions. Although the relationship between Christian slaves under the yoke and pagan masters is difficult, they are to continue to live by the rules of slavery. The fact that they have a higher Lord (Col 3:22-25) does not release them from this obligation. It obligates them all the more to be models of obedience, for this service to human masters is simultaneously service to the Lord.
Yet Paul's chief concern and chief rationale in issuing these instructions is mission. The purpose (so that) of the slaves' respectable conduct is protection of God's name and the Christian message (compare Tit 2:10). The danger of disrespectful attitudes toward social institutions is that the intention of the gospel will be totally misunderstood and the church's evangelistic mission incapacitated.
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