Romans 7:14-25 is describing the person who wants to do what is good and right but is still under the bondage of sin. On the one hand he desires to follow the Spirit, but due to his human weakness he keeps yielding to the desires of the flesh. The solution is found in Romans 7:24-25 where Paul writes, 'O wretched man that I am! Who will deliver me from this body of death? I thank God -- through Jesus Christ our Lord! So then, with the mind I myself serve the law of God, but with the flesh the law of sin.'
This solution is explained in greater detail in chapter 8.
To serve the law of sin 'with the flesh' versus serving the law of God 'with the mind' is explained as, 'For those who live according to the flesh set their minds on the things of the flesh, but those who live according to the Spirit, the things of the Spirit' (v.5).
To experience complete victory over sin, we must humble ourselves before Jesus and deliberately set our minds on spiritual things. If we do not, we will continue to keep our minds focused on the things of the flesh and continue to yield to temptation.
but with the flesh the law of sin