"All things which are good cometh of God," (Ether 4:12). Moroni therefore draws the only logical conclusion, "Whatsoever thing is good is just and true." (v. 6)
The words of the Lord, spoken by all His holy prophets, are good tidings; they are just and true. Speaking of these words to Moroni, the Lord said: "I am He Who speaketh." (Mosiah 2:34-35)