5 Bondservants, be obedient to those who are your masters according to the flesh, with fear and trembling, in sincerity of heart, as to Christ;
6 not with eyeservice, as men-pleasers, but as bondservants of Christ, doing the will of God from the heart,
7 with goodwill doing service, as to the Lord, and not to men,
8 knowing that whatever good anyone does, he will receive the same from the Lord, whether he is a slave or free.
9 And you, masters, do the same things to them, giving up threatening, knowing that your own Master also is in heaven, and there is no partiality with Him.
bondservants (v.5) = slaves
In many of the cities of Asia Minor, slaves outnumbered freemen. Many questions would inevitably arise with regard to the duties of masters and servants in a state of society in which slavery prevailed and had the sanction of ancient and undisputed use. Especially would this be the case when Christian slaves (of whom there were many) had a heathen master, and when the Christian master had heathen slaves. Hence the considerable place given in the New Testament to this relation and the application of Christian principles (1 Corinthians 7:21-22; 1 Timothy 6:1-2; Titus 2:9-10; and Philemon, in addition to Colossians 3:22, 4:1, and 1 Peter 2:18-25). Here, as elsewhere in the New Testament, slavery is accepted as an existing institution, which is neither formally condemned nor formally approved. — Wuest, pg. 138.
according to the flesh (v.5) — distinguishes earthly masters who are over material and earthly matters only as opposed to Christ, who is also Master of spiritual things
fear and trembling (v.5) = solicitous zeal, anxious care not to fall short of the standard
in sincerity of heart (v.5) = with inward reality, sincerity and with an undivided heart — it qualifies “be obedient” not “with fear and trembling.”
eyeservice (v.6) = service done only when under the master’s eye — obedience to save appearances and gain undeserved favor
heart (v.6) = soul
masters (v.9) — Christian lords and masters of slaves
do the same things (v.9) — treat them with the same Christian principles
partiality (v.9) — the fault of one who when called on to requite or give judgment has respect to the outward circumstances of men and not to their intrinsic merits, and so prefers, as the more worthy, one who is rich, high-born, or powerful, to another who is destitute of such gifts. — Wuest, page 139