The moral soundness, the integrity and uprightness, of the Nephite Saints of God unto whom Mormon declared His holy word, delighted Mormon's soul. Seeing their good works, he rejoiced in the words of the Lord, Who when speaking of false prophets "who come to you in sheep's clothing, but inwardly they are ravening wolves," said of them: "Ye shall know them by their fruits. Do men gather grapes of thorns, or figs of thistles? Even so every good tree bringeth forth good fruit; but a corrupt tree bringeth forth evil fruit. A good tree cannot bring forth evil fruit neither a corrupt tree bring forth good fruit. Every tree that bringeth not forth good fruit is hewn down, and cast into the fire. Wherefore, by their fruits ye shall know them." (III Nephi 14:16-20)
The works men do are like the fruit a tree brings forth. Mormon took great comfort and an unceasing joy in that his brethren were like unto good trees; their works were good, so as the Savior said, "they were also good."