What does Romans 6:13 tell believers not to do with their members?

Romans 6:13 instructs believers not to yield their members—the functions of the body—as instruments of unrighteousness unto sin, that is, unto the old Adam or old sin nature. They are not to give in to sin but to yield themselves unto God as instruments of righteousness.

Les explains that Romans 6:13 says, "neither yield your members as instruments of unrighteousness unto sin," meaning don't give in to the old Adam, the old sin nature. The members are of the flesh, the functions of the body. It is up to us because we have free will; God does not force obedience, but the indwelling Spirit constantly urges. The flip side is to yield yourselves unto God as those alive from the dead, and your members as instruments of righteousness unto God.

Romans 6:13

Neither yield ye your members as instruments of unrighteousness unto sin: but yield yourselves unto God, as those that are alive from the dead, and your members as instruments of righteousness unto God.

What does Paul mean by the word "sin" in Romans 6:13?

In Romans 6:13, Paul uses 'sin' to mean the old Adam, the old sin nature. It is not merely an isolated act but the indwelling principle within the members of the flesh. He urges believers not to yield their bodily members as instruments of unrighteousness to that sin nature.