Those who have believing masters, let them not despise them, because they are brothers, but rather let them serve them, because those who partake of the benefit are believing and beloved. Teach and exhort these things.
They that partake of the benefit ... as rendered here indicates the masters, who, because they are believing and beloved, should receive of this better service.  Some commentators render the words differently, applying them to the slaves, who by better service may receive more considerate treatment.  As a matter of fact, both interpretations are true. The principle is also applicable to all human relations and all human institutions, regardless of their desirability.  Christianity pours in the oil that lubricates and improves even the most unsavory situations.