Translation:

64. And We sent down the Book to thee for the express purpose that thou shouldst make clear to them those things in which they differ and that it should be a guide and a mercy to those who believe.

Notes (Tafseer)

2091. But the path of duty before Allah's Messenger is clear. He is sent with the Revelation (the Qur-an) for three express purposes; (1) that he should bring about unity among the jarring sects, for the Gospel of Unity, while preaching the One True God, leads also to the unity of mankind; (2) that the revelation should be a guide to right conduct; and (3) that it should show the path of repentance and Salvation, and thus be the highest mercy to erring sinners.