Mormon’s introduction to his letter to his son is somewhat formal, particularly compared to the tone we will see in the letter in Moroni 9. The reason is that Mormon is writing to his son as part of his recent call to the ministry. This is an administrator’s letter first, and secondly, a letter to his son.
Therefore, Mormon’s content in the introduction is about his ministry and the fact that Mormon is praying for him in the execution of that ministry. That ends the personal aspect of the letter. Verse 3 turns to business. Mormon understands that there have been disputations, and he needs to quell them. This suggests that it is Moroni’s new responsibility to do so, and his father is providing the information that he is to teach to quell the disputations.
The historical implication of the letter itself is that Mormon and Moroni were, at the time, in very separate regions. Mormon was leading an army, and Moroni may have been laboring in a city that was deeper in Nephite territory. Eventually, as the Nephites were swept up to Cumorah, the two were reunited, but that is after this letter.