John Piper on William Wilberforce:

   But he was practical with a difference. He believed with all his heart that new affections for God were the key to morals and lasting political reformation. And these new affections and this reformation did not come from mere ethical systems. They came from what he called the “peculiar doctrines” of Christianity. For Wilberforce, practical deeds were born in “peculiar doctrines.” By that term he simply meant the central distinguishing doctrines of human depravity, divine judgment, the substitutionary work of Christ on the cross, justification by faith alone, regeneration by the Holy Spirit, and the practical necessity of fruit in all life devoted to good deeds.

The Fatal Habit of Nominal Christians

He wrote his book [A Practical View of Christianity] to show that the “bulk” of Christians in England were merely nominal because they had abandoned these doctrines in favor of a system of ethics and had thus lost the power of ethical life and the political welfare. He wrote:

The fatal habit of considering Christian morals as distinct from Christian doctrines insensibly gained strength. Thus the peculiar doctrines of Christianity went more and more out of sight, and as might naturally have been expected, the moral system itself also began to wither and decay, being robbed of that which should have supplied it with life and nutriment.

   He pled [sic] with nominal Christians of England not to turn “their eyes from the grand peculiarities of Christianity, [but] to keep these ever in view, as the pregnant principles whence all the rest must derive their origin, and receive their best support.”
   Knowing that Wilberforce was a politician all his adult life, who never lost an election from the time he was twenty-one years old, we might be tempted to think that his motives were purely pragmatic—as if he should say, “If Christianity works to produce the political welfare, then use it.” But that is not the spirit of his mind or his life. In fact, he believed that such pragmatism would ruin the very thing it sought, the reformation of culture.

—John Piper, The Roots of Endurance, pp.119–121