A. T. Robertson,
Studies in the Epistle of James
“ The theory that James and the other brothers and sisters were all children of Joseph by a former marriage (step-brother theory) is free from the difficulty about the word “brother” and is not inconceivable in itself. Unfortunately there are critical objections to it, for Jesus is not called “only begotten” of Mary but “firstborn” in Luke 2:7: “She brought forth her firstborn son.”Jesus is “only begotten” of God (John 1:18) , as the widow of Nain had an only son (Luke 7:12) and Jairus an only daughter (Luke 8:42) . ”
