4:2 Sun of righteousness. The Sun of righteousness is none other than the Lord Jesus Christ returning to His world in its darkest night. He is “the light of the world” (John 8:12), both physically (“upholding all things by the word of His power”—Hebrews 1:3) and spiritually (“the light of the knowledge of the glory of God in the face of Jesus Christ”—II Corinthians 4:6).
4:2 healing in his wings. This is the normal Hebrew word for “wings,” but it could possibly be understood as “rays,” since it is translated various ways and seems to have the basic meaning of “projecting.”