Mormon’s statement in verse 5, “For I remember the word of God which saith by their works ye shall know them; for if their works be good, then they are good also,” echoes the words of the Savior at the Temple, in 3 Nephi 14:16–20. There Jesus said, “Ye shall know them by their fruits. … A good tree cannot bring forth evil fruit, neither a corrupt tree bring forth good fruit. … Wherefore, by their fruits ye shall know them.”
Mormon, however, says, “By their works ye shall know them.” Whereas the Savior commonly used metaphors to illustrate principles, Mormon tended to use a more straightforward style of sentence structure, unembellished and very plain. His adaptations of the text come predominately through developing the concepts and principles to benefit his audience. He often added a new level of understanding to the words and phrases. In this case, the word “works” is more active, progressive, and ongoing, whereas “fruits” might be thought of as more final, specific, and result oriented.
Following this reference to the Savior’s sermon, Mormon went on to develop the thought even further. He explained that if their works were good, then they were good. He said, in verse 10, “Behold, God has said, a man being evil cannot do that which is good.” This refers back to Jesus’s metaphor of the tree in 3 Nephi 14:17–19, in which a tree, being a good tree, cannot bring forth evil fruit. Mormon continued, “For if he offereth a gift or prayeth unto God, except he shall do it with real intent, it profiteth him nothing.”
Giving a gift, making an offering, or praying without real intent (i.e. doing so casually or grudgingly) is not counted as righteousness and one might as well not have performed the “righteous” action at all. Such gifts or offerings can be meaningfully compared to the giving of tithing today. In Mormon 2:14, Mormon had recorded that the people had refused to offer the ultimate and most desirable sacrifice—that of a broken heart and contrite spirit. Notice further that Moroni reused the words “with real intent” in his encouragement to pray to know the truth of the Book of Mormon in Moroni 10:4–5. Moroni had learned this from his father.