The metamorphosis of a Jewish sect into the ecumenical Christian Church is indeed astonishing; but so, too, is the metamorphosis of the Indian Theravadin Buddhist philosophy into the ecumenical Mahayanian Buddhist religion. The strength of the Mahayana as a missionary religion lay in its devotees’ willingness to come to terms with the pre-existing religions of the areas that the Mahayanian missionaries evangelized. The Mahayana was not inhibited by anything in its Theravadin Buddhist past from being frankly tolerant and from overtly aiming, not at conquest, but at symbiosis. On the other hand, Christianity’s Jewish past was a handicap for Christian theologians and missionaries. Christianity could not bring itself to live and let live; it had either to destroy its rivals or to absorb them; and it would absorb them only in so far as it could do this covertly. Yet Christianity absorbed far more than it destroyed. In fact, its method of propagating itself was more Mahayana-like than its official representatives could afford to admit.
Mankind and Mother Earth, A Narrative History of the World, OUP, 1976, posthumous