Jamieson, Fausset & Brown, on 1Cor 7:21

care not for it--Let it not be a trouble to thee that thou art a servant or slave. use it rather--Continue rather in thy state as a servant (Co1 7:20; Gal 3:28; Ti1 6:2). The Greek, "But if even thou mayest be made free, use it," and the context (Co1 7:20, Co1 7:22) favors this view [CHRYSOSTOM, BENGEL, and ALFORD]. This advice (if this translation be right) is not absolute, as the spirit of the Gospel is against slavery. What is advised here is, contentment under one's existing condition (Co1 7:24), though an undesirable one, since in our union with Christ all outward disparities of condition are compensated (Co1 7:22). Be not unduly impatient to cast off "even" thy condition as a servant by unlawful means (Pe1 2:13-18); as, for example, Onesimus did by fleeing (Plm 1:10-18). The precept (Co1 7:23), "Become not (so the Greek) the servants of men," implies plainly that slavery is abnormal (compare Lev 25:42). "Men stealers," or slave dealers, are classed in Ti1 1:10, with "murderers" and "perjurers." NEANDER, GROTIUS, &c., explain, "If called, being a slave, to Christianity, be content--but yet, if also thou canst be free (as a still additional good, which if thou canst not attain, be satisfied without it; but which, if offered to thee, is not to be despised), make use of the opportunity of becoming free, rather than by neglecting it to remain a slave." I prefer this latter view, as more according to the tenor of the Gospel, and fully justified by the Greek.