This is a wonderful and historically important piece of ephemera. Legh Richmond [1772-1827], writes here in the blossom of his career. This is apparently THE introductory letter between Wilberforce and Richmond, and it occupies a whopping 7.5pp of extensive handwritten content.

They would go on to become such close friends in the cause of the poor, working class, women, children, and the abolition of the slave trade that Richmond would name his son Wilberforce Richmond. Richmond was author of one of the great devotional tales of the time, almost continuously in print, The Dairyman's Daughter, which Richmond dedicated to William Wilberforce!

Richmond writes this letter to Wilberforce in response to reading his "Practical View of Christianity." The work was a lightning rod for Richmond's own Christianity and ministry. He likely read the first edition, just published in 1797. 

They just don't come on the market like this very often! Perfect piece demonstrating the impact of Wilberforce's "Practical View." 

Date: November 13, 1799.

Extracts: 

Commenting on the "Practical View:" "I am from my heart convinced that no effective reformation can take place either in the world at large or in the microcosm of our own soul, which is not laid in Christian virtue, by which term I understand the imitation of the conduct and maxims of Christ, produced, nourished, and perfected by the enlivening grace of the Holy Spirit operating upon the heart of the believer; and though from the very nature and definition of such virtue, it can only proceed from the free gift of God, when where and to whom He pleases; yet, as his precious treasure is committed to earthly vessels, and he is graciously pleased to make and appoint humble mortals to be ministers of his promised blessings, there arises a most urgent call from hence to all that are embarked in the propagation of the Gospel to be diligent and unremitting in their endeavour to bring their brethren to the knowledge of the truth as it is in Christ Jesus. . . 

For my part, I bless God, that you have been the instrument of all some at least to a sense of the serious nature of the ministerial office and of the whereunto they officiate. May the God of grace  accompany your work with his blessing wherever it shall go, and may that same vital spirit of religion, which is therein so powerfully recommended, be poured out abundantly throughout the country in which we live to the everlasting benefit of multitudes.

He further mentions Hannah More, the doctrine of election, the Trinity, the publication of his sermon [which occasioned their introduction], his own testimony of experimental religion, etc.