They generally did it only partially, through an "emanation," not through a complete descent. It is said, for instance, that Vivekananda was an incarnation (a vibhuti) of Shiva's; but Shiva himself ... I have had a very close relationship with him and he clearly expressed the will to come down on earth only with the supramental world. When the earth is ready for supramental life, he will come. And almost all those beings will manifest - they are waiting for that moment, they do not want the present struggle and darkness. page 19 , Mother's Agenda , volume 6 , 12th Jan - 1965