The Fulness of the Gospel
The Book of Mormon is said to have “the fulness of the gospel of Jesus Christ” or “the fulness of the everlasting gospel” (D&C 20:9; 27:5; 135:3; Joseph Smith History 1:34), yet it does not mention such key beliefs as baptism for the dead, eternal marriage, and exaltation, so it can’t contain the “fulness of the gospel.”
If the term “gospel” meant all truth from God, as both Latter-day Saints and other Christians most often use it, that criticism would be valid. But the restored Church teaches that we do not possess all truth, which only God possesses. Were it otherwise, we would have no need of living prophets and no need to declare that “We believe all that God has revealed, all that He does now reveal, and we believe that He will yet reveal many great and important things pertaining to the Kingdom of God” (Article of Faith 9).
Since it is impossible for us to possess all of God’s truth in mortality, we must look for another meaning for “fulness of the gospel” based not on how the term “gospel” is commonly used, but on how the Lord uses the term. In the scriptures restored or revealed to Joseph Smith, the term “gospel,” an old English word meaning “good news,” specifically refers to the atonement of Christ. This is the definition given in 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; 76:40-42; 84:26-27; 107:20; 135:3; 138:2-4, 57), and the Pearl of Great Price (Joseph Smith-History 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 and complete explanation of the atonement of Christ and therefore clearly qualifies as containing the fulness of the gospel. Of particular importance in explaining the atonement are chapters 2 and 9 of 2 Nephi, Mosiah 15, and chapters 34 and 42 of Alma.