12 Therefore do not let sin reign in your mortal body, that you should obey it in its lusts.
With verse 12 the discussion moves from our union with Christ to how to live daily under our position in Christ.
The “therefore” here is the conclusion from verse 11, not further reflection. After we “reckon” ourselves by faith positionally dead with Christ, we have the responsibility to deal with sin controlling our lives.
Christians can exercise their volition against sin and not let it dominate their lives. There is a close connection between our status with God and what we do with that status.
do not let [present tense—ongoing] sin reign [as king]
God commands us (imperative mood) to not let “sin reign” in our mortal bodies. We can translate the Greek as: “Stop letting sin reign in your mortal body.” The words “stop letting” is an issue of volition. The assumption is that sin reigns already in the believer and he needs to stop letting it happen.
The word “let” assumes sin is still in the life of the believer. Sin is still a force in the Christian life but it is not absolute. There is no need to live as a slave to sin. The idea that “let” is a command challenges us to become what we are. We live our daily lives on the truth that we died to sin and are alive to God (v. 11).
Sin is personified as a dethroned King who seeks his throne, his former place of reigning. Sin lost its reign when the believer became identified with Christ. We saw the idea of “reign” in 5:21:
Ro 5:21, so that as sin reigned in death, even so grace might reign through righteousness to eternal life through Jesus Christ our Lord.
The contrast is between sin reigning and grace reigning. The theme running through chapters five and six is living out the grace of God. Grace always precedes its application to life. Christians live under the giving grace of God, which does not allow sin to become our master.
in your mortal [dying] body [life],
“Mortal body” here is not simply the physical body but the man as a whole, including the body itself. Sin is a temporary dynamic; we need to keep eternal values in view. It is a dynamic that will pass away with time. The Christian has an immortal soul but not an immortal body. Our body is not yet redeemed.
Note the plural “your” and the singular “body.” “Body” here refers to the believer’s current life in time walking with the Lord.
All Christians struggle against sin all their lives.
There is no such thing as perfectionism in the Christian life; however, there is such a thing as victory over sin. It is possible for sin to reign or dominate a Christian. Some give themselves to cravings and lusts. There is a defeatism in some believers because they cannot measure up to their own false assumption of perfectionistic standards.
It is not necessary for sin to dominate the Christian life. We now have new life in Christ and the power that comes with that. The argument of Romans six is about dealing with sin biblically. As we will see in coming studies, we can offer ourselves as instruments of righteousness to God (Ro 6:13).