What is Sancho's purpose for writing?

to convince Sterne that Africans can be religious and spiritualto convince Sterne that he is a formerly enslaved person from the coloniesto convince Sterne to write more texts against slavery to convince Sterne to create more characters like uncle Toby

To show that he is sympathetic to sancho's cause.

Based on the given excerpt related to this question, the purpose of Sancho's writing is to convince Sterne to write more texts against slavery. This is based on the excerpt from Letters of the Late Ignatius Sancho, an African who wants to tell the public about the pain and mistreatment in slavery.