I speak after the manner of men - I speak as people usually speak; or I draw an illustration from common life, in order to make myself better understood.
Because of the infirmity of your flesh - The word “infirmity” means weakness, feebleness; and is opposed to vigor and strength. The word “flesh” is used often to denote the corrupt passions of people; but it may refer here to their intellect, or understanding; “Because of your imperfection of spiritual knowledge; or incapacity to discern arguments and illustrations that would be more strictly spiritual in their character.” This dimness or feebleness had been caused by long indulgence in sinful passions, and by the blinding influence which such passions have on the mind. The sense here is, “I use an illustration drawn from common affairs, from the well-known relations of master and slave, because you will better see the force of such an illustration with which you have been familiar, than you would one that would be more abstract, and more strictly spiritual.” It is a kind of apology for drawing an illustration from the relation of master and slave.
For as ye have yielded - Note, Romans 6:13. Servants to uncleanness. Have been in bondage to impurity. The word “uncleanness” here refers to impurity of life in any form; to the degraded passions that were common among the heathen; see Romans 1.
And to iniquity - Transgression of law.
Unto iniquity - For the purpose of committing iniquity. It implies that they had done it in an excessive degree. It is well for Christians to be reminded of their former lives, to awaken repentance, to excite gratitude, to produce humility and a firmer purpose to live to the honor of God. This is the use which the apostle here makes of it.
Unto holiness - In order to practice holiness. Let the surrender of your members to holiness be as sincere and as unqualified as the surrender was to sin. This is all that is required of Christians. Before conversion they were wholly given to sin; after conversion they should be wholly given to God. If all Christians would employ the same energies in advancing the kingdom of God that they have in promoting the kingdom, of Satan, the church would rise with dignity and grandeur, and every continent and island would soon feel the movement. No requirement is more reasonable than this; and it should be a source of lamentation and mourning with Christians that it is not so; that they have employed so mighty energies in the cause of Satan, and do so little in the service of God. This argument for energy in the divine life, the apostle proceeds further to illustrate by comparing the rewards obtained in the two kinds of servitude, that of the world, and of God.