Jamieson, Fausset and Brown on Matthew 10:28

28. And fear not them which kill the body, but are not able to kill the soul--In Lu 12:4, "and after that have no more that they can do."

but rather fear him--In Luke (Lu 12:5) this is peculiarly solemn, "I will forewarn you whom ye shall fear," even Him

which is able to destroy both soul and body in hell--A decisive proof this that there is a hell for the body as well as the soul in the eternal world; in other words, that the torment that awaits the lost will have elements of suffering adapted to the material as well as the spiritual part of our nature, both of which, we are assured, will exist for ever. In the corresponding warning contained in Luke (Lu 12:4), Jesus calls His disciples "My friends," as if He had felt that such sufferings constituted a bond of peculiar tenderness between Him and them.