The declaration of Christ as the light of the world is entirely appropriate, and particularly poignant as these people undergoe three days of suffocating darkness. Physically and symbolically, they are in need of the light of the world.
Translation: It is unclear what the original plate text behind “I am Alpha and Omega, the beginning and the end” might have been. They certainly could not be directly translated by these words, as they depend upon the Greek alphabet. This is a New Testament phrase found in the book of Revelation (for example, Revelation 1:8,11). Alpha is the first letter in the Greek alphabet and omega the last. Thus the intent of the phrase is to be all encompassing. The intent would be to say that Christ was all that we needed, but this particular phrase is absolutely dependent upon the New Testament and its presence in our Book of Mormon is obviously dependent upon Joseph Smith’s familiarity with that phrase.
What seems to be happening in this case is that there is a meaning that is presented to Joseph, and he “translates” that meaning using words and phrases that communicate that message based on the worldview he has as he writes.