This is one name of the Son of God, denoting a divine attribute. The Prophet Malachi (4:2) refers to Jesus as the "Sun of Righteousness," to express His equality with the Father. Speaking of the Lord's day, the Hebrew prophet says it shall burn up all the proud and all that do iniquity; they shall be stubble; but unto those who fear the Lord's name, "shall the Sun of Righteousness arise with healing in His wings." Malachi seems to have borrowed a figure of speech suggested by the winged sun in Egyptian mythology, especially the Osiris myth; and in other eastern religions featuring sun worship.
The Jews at the time of Malachi must have been familiar with those religious concepts and symbols. Moroni here uses an original name, Son of Righteousness, which reminds us of Jeremiah 23:6: "And this is the name whereby He shall be called, THE LORD OUR RIGHTEOUSNESS." This is His name. The Sun of Righteousness is only the symbol of the Name. Commentators have suggested that the expression of Malachi does not refer to the Lord, or any other person, but to a principle. In the text before us it is made clear that the Son of Righteousness is none other than our Lord, Jesus Christ, Himself.