Satan’s tactic of stirring the Nephites up to anger when repentance was preached to them (v. 3) was also identified by Nephi, son of Lehi (see 2 Nephi 28:19–20). When Mormon spoke with sharpness, he was probably moved upon by the Holy Ghost (see D&C 121:43), and this was the cause of their trembling (see D&C 85:6). Nevertheless, Satan was there to stir them up to anger, thus Mormon feared that they had lost the Spirit of the Lord (Moroni 9:4). Other evidences are also cited by Mormon to support this conclusion (v. 5).
Mormon encouraged his son Moroni to act by laboringly diligently, and not to re-act by reciprocating (v. 6; see also 2 Nephi 2:13–16). How we act or re-act will bring our souls to rest in the kingdom of God, or bring about our condemnation (Moroni 9:6). We each have a mission in life, and the admonition given by Mormon is applicable to all.