New Defender's Study Bible Notes
6:5 Servants. See also the similar passage in Colossians 3:22-25. The “servants” here are actually “bond-servants” or “slaves.” Although the institution of slavery seems repugnant to us today, and certainly inconsistent with Christian ideals, it was a basic part of social order in the ancient world, impossible to eliminate without a revolutionary overturning of the entire society. Consequently, neither Paul nor the other apostles nor even Jesus Himself ever argued against it. Rather they urged true Christian behavior on the part of both master and slave, and eventually these principles would change society itself, as an indirect effect.
6:5 trembling. This is an idiomatic expression indicating serious recognition of the importance of a given responsibility, used by Paul of his own attitude in preaching the gospel (I Corinthians 2:3).