"We are consistently taught that The Book of Mormon is the `most correct book' and that it contains the truth, the Word of God, and the fullness of the gospel (Doctrine and Covenants 19:26; 20:9; 27:5; 42:12; 135:3). Exactly where in The Book of Mormon are the following doctrines or concepts taught?
Response by John A. Tvedtnes
There are two questions here: 1) In what way is the Book of Mormon "the most correct book"? and 2) If the Book of Mormon contains the "fulness of the gospel," why does it not discuss the important doctrines in the list.
1) The Most Correct Book
Correctness need not refer to the translation, the grammar, or the spelling, only to the content, notably the doctrine. No one language can adequately express all the nuances intended by the original. Anyone who knows a foreign language can attest that there is no one-to-one correspondence between words in two different languages. Thus, for example, the Hebrew word meaning "to sit" also means "to dwell." Seeing this word in a Hebrew text, a translator would have to decide which of the two English verbs to use in his English language version. In 1 Nephi 1:6, we read that "there came a pillar of fire and dwelt upon a rock before him." In this case, Joseph Smith used the word "dwelt" where another translator might have preferred "sat."
Since Joseph later made corrections to the text of the Book of Mormon, on both copies of the manuscript (the original and the copy prepared for the printer) and in later editions, it seems clear that he did not consider the book to be an infallible translation. The Book of Mormon itself indicates that it may contain errors made by the men who wrote it (Title Page; 1 Nephi 19:6; Jacob 1:2; 7:26; Mormon 8:1, 17; 9:31-33; 3 Nephi 8:2; Ether 5:1). Since Joseph Smith must have known about these statements, his declaration of correctness could not have meant that the book had no failings whatsoever. A closer examination of his declaration supports this idea:
Since the context of the prophet's remarks was "abiding by [the] precepts" found in the Book of Mormon, it is clear that he was speaking about its teachings rather than its language or history.
2) Fulness of the Gospel
Although Latter-day Saints frequently use the term "gospel" to refer generally to all truths to be learned through the restored Church, this is not the real meaning of the term. The gospel is the good news of Christ's atonement, and its first principles are faith, repentance, baptism, and receiving the Holy Ghost. This is the definition given in both the Book of Mormon (1 Nephi 10:14; 15:13-14; 3 Nephi 27:13-21; Ether 4:18), the Doctrine and Covenants (D&C 3:20; 13:1; 20:9; 27:5; 33:11-12; 39:5-6; 42:12; 76:40-42; 84:26-27; 107:20; 135:3; 138:2-4, 57), and the Pearl of Great Price (JS-H 1:34; Articles of Faith 3-4). D&C 93:51 uses the term "the gospel of salvation," while Abraham 2:11 speaks of "the blessings of the Gospel, which are the blessings of salvation, even of life eternal" (cf. D&C 128:5, 17). In Jacob 7:6, the gospel is defined as "the doctrine of Christ," referring to the doctrine concerning Christ, rather than the totality of Christ's teachings, since he had not yet been born when these words were uttered (cf. Mormon 3:21; D&C 76:82). Elsewhere, the Book of Mormon equates the "fulness of the gospel" with coming "to the knowledge of the true Messiah" (1 Nephi 10:14; 15:13-14; cf. 3 Nephi 20:30-31; D&C 19:27). The Book of Mormon contains the most lucid explanation of the atonement of Christ (see especially 2 Nephi 2, 9; Mosiah 15; Alma 34, 42) and therefore clearly qualifies as containing the fulness of the gospel.
Also, please see Dr. Sidney B. Sperry's comments on the subject here.