George Eldon Ladd, "The Kingdom of God--Reign or Realm?" JBL 81 (1962): 230-238.

Jesus' understanding of the "kingdom" is not the apocalyptic "realm" but rather God's "rule." Jesus, therefore, followed the rabbinic usage rather than the apocalyptic, with several variations, the most important of which is the fact that the kingdom is dynamically present in His person and mission instead of the Torah.