Римлянам 6:19

I speak after the manner of men--descending, for illustration, to the level of common affairs. because of the infirmity of your flesh--the weakness of your spiritual apprehension. for as ye have yielded--"as ye yielded," the thing being viewed as now past. your members servants to Uncleanness and to Iniquity unto--the practice of iniquity; even so now yield your members servants to Righteousness unto holiness--rather, "unto (the attainment of) sanctification," as the same word is rendered in Th2 2:13; Co1 1:30; Pe1 1:2 : --that is, "Looking back upon the heartiness with which ye served Sin, and the lengths ye went to be stimulated now to like zeal and like exuberance in the service of a better Master."

The apostle having at large asserted, opened, and proved, the great doctrine of justification by faith, for fear lest any should suck poison out of that sweet flower, and turn that grace of God into wantonness and licentiousness, he, with a like zeal, copiousness of expression, and cogency of argument, presses the absolute necessity of sanctification and a holy life, as the inseparable fruit and companion of justification; for, wherever Jesus Christ is made of God unto any soul righteousness, he is made of God unto that soul sanctification, Co1 1:30. The water and the blood came streaming together out of the pierced side of the dying Jesus. And what God hath thus joined together let not us dare to put asunder.

6:19 Paul uses the Greek word sarx (human nature, or flesh) to refer to the frailty and proneness to sin that characterizes humans. Paul uses the illustration of slavery to show the relationship of the human nature to sin.