A study about the verse of Introduction (5:67)

In this essay, the verse of "introduction" and "deliverence" is explained according to Shia and Sunni commentaries. Meantime, by relying on the traditions, relation with the divine leaderahip (Imamat) of Amirul-Momenin Ali (p.b.u.h), is announced, different aspects of its characteristics (time, and cause of descendence) are studied.Then, the author, has explained the relation between this verse and its previous and next verses, that talk about the people of Book, in the form of questions and answers.