John Calvin on Romans 8:7
Behold the power of free-will! which the Sophists cannot carry high enough. Doubtless, Paul affirms here, in express words, what they openly detest, — that it is impossible for us to render our powers subject to the law. They boast that the heart can turn to either side, provide it be aided by the influence of the Spirit, and that a free choice of good or evil is in our power, when the Spirit only brings help; but it is ours to choose or refuse. They also imagine some good emotions, by which we become of ourselves prepared. Paul, on the contrary, declares, that the heart is full of hardness and indomitable contumacy, so that it is never moved naturally to undertake the yoke of God; nor does he speak of this or of that faculty, but speaking indefinitely, he throws into one bundle all the emotions which arise within us. Far, then, from a Christian heart be this heathen philosophy respecting the liberty of the will. Let every one acknowledge himself to be the servant of sin, as he is in reality, that he may be made free, being set at liberty by the grace of Christ: to glory in any other liberty is the highest folly.