I find then a law, that, when I would do good, evil is present with me. I find then a law - I am in such a condition and state of soul, under the power of such habits and sinful propensities, that when I would do good - when my will and reason are strongly bent on obedience to the law of God and opposition to the principle of sin, evil is present with me, κακον παρακειται, evil is at hand, it lies constantly before me. That, as the will to do good is constantly at hand, Romans 7:18, so the principle of rebellion exciting me to sin is equally present; but, as the one is only will, wish, and desire, without power to do what is willed, to obtain what is wished, or to perform what is desired, sin continually prevails.
The word νομος, law, in this verse, must be taken as implying any strong or confirmed habit, συνηθεια, as Hesychius renders it, under the influence of which the man generally acts; and in this sense the apostle most evidently uses it in Romans 7:23.