If you want to read the entire letter, you can see it in the Times and Seasons, or on lds.org at this link: https://www.lds.org/ensign/2002/07/the-wentworth-letter?lang=eng
And thanks to the Correlation Departments, you can't read the entire letter in the lesson manual because the following passage was omitted:
“Through the medium of the Urim and Thummim I translated the record by the gift and power of God.… This book … tells us that our Savior made His appearance upon this continent after His resurrection;"
Original letter (showing the omitted portions in red):
"Through the medium of the Urim and Thummim I translated the record by the gift and power of God.
"In this important and interesting book the history of ancient America is unfolded, from its first settlement by a colony that came from the Tower of Babel at the confusion of languages to the beginning of the fifth century of the Christian era. We are informed by these records that America in ancient times has been inhabited by two distinct races of people. The first were called Jaredites and came directly from the Tower of Babel. The second race came directly from the city of Jerusalem about six hundred years before Christ. They were principally Israelites of the descendants of Joseph. The Jaredites were destroyed about the time that the Israelites came from Jerusalem, who succeeded them in the inheritance of the country. The principal nation of the second race fell in battle towards the close of the fourth century. The remnant are the Indians that now inhabit this country. This book also tells us that our Savior made His appearance upon this continent after His Resurrection;"