It is very interesting to evaluate what can be extracted from the writings in Mormon chapter 3 that may indicate when Mormon wrote this epistle to Moroni, who did not note an exact date, just that it was “soon after my calling to the ministry.” The dating evidence is circumstantial, but there are enough matching pieces in each text to estimate that it was written close to the same period that Mormon addressed in Mormon chapter 3, which was just after the conclusion of the ten-year peace. Having enjoyed learning and working together with Mormon as his assistant in making plates, reading records, selecting passages to include in the abridgment, and discussing with him the spans of Nephite and Jaredite history, Moroni would have been about 29 years old in AD 362. At that time, he could have been sent out to work in the wider field of the church, especially as serious problems were already brewing.
In Mormon 3, the prophet Mormon had been commanded to preach repentance to the people. In Mormon’s letter recorded in Moroni 8, the words repent and repentance were used twelve times, five as a verb and seven as the noun. This builds upon the two nouns and one verb found in Mormon 3. Since repentance was a pressing matter at this time, it is quite possible that he wrote this letter during his period of being an idle witness.
Although Moroni 8 is commonly thought of as only being about the baptism of infants, it is also about repentance. The dominant refrain is “Repent! Repent!” Sinners are called to repentance; parents must teach repentance; parents must repent; little children need no repentance. The whole letter circles back to the issue of repentance. Little children should not be baptized because they cannot repent. They do not need to repent. They are unable to repent. The first fruits of repentance are baptism. One may not, then, baptize children until they are able to repent. Repentance makes baptism and the atonement meaningful.
Joseph M. Spencer, “On the Dating of Moroni 8–9,” Interpreter: A Journal of Latter-day Saint Faith and Scholarship 22 (2016): 131–148.
Alan C. Miner, “A Chronological Setting for the Epistles of Mormon to Moroni,” Journal of Book of Mormon Studies 3, no 2. (1994): 94–113.