What God Requires

The demand in Romans 8:13 is not sinlessness but mortal combat with sin. This is utterly essential in the Christian life. Otherwise we give no evidence that the flesh has been crucified. And if the flesh has not been crucified we do not belong to Christ (Galatians 5:24). The stakes in this battle are very high. We are not playing war games. The outcome is heaven or hell.

How then do dead people "put to death the (sinful) deeds of the body"? We have answered, "By faith!" But just what does this mean? How do you fight sin with faith?

Suppose I am tempted to lust. Some sexual image pops into my brain and beckons me to pursue it. The way this temptation gets its power is by persuading me to believe that I will be happier if I follow it. The power of all temptation is the prospect that it will make me happier. No one sins out of a sense of duty, when what they really want is to do right.

So what should I do? Some people would say, "Remember God's command to be holy (1 Peter 1:16) and exercise your will to obey because he is God!" But something crucial is missing from this advice, namely, FAITH. A lot of people strive for moral improvement who cannot say, "The life I live I live BY FAITH" (Galatians 2:20). A lot of people try to love who don't realize that, "What counts is FAITH working through love" (Galatians 5:6).

The fight against lust (or greed or fear or any other temptation) is a fight of faith. Otherwise the result is legalism.

John Piper - How Dead People Do Battle with Sin