Bertrand Russell says,
“The Christian religion, as it was handed over by the late Roman Empire to the barbarians, consisted of three elements: first, certain philosophical beliefs, derived mainly from Plato and the Neoplatonists, but also in part from the Stoics; second, a conception of morals and history derived from the Jews; and third, certain theories, more especially as to salvation, which were on the whole new in Christianity, though in part traceable to Orphism*, and to kindred cults of the Near East.
The most important Jewish elements in Christianity appear to me to be the following:
• I. A sacred history, beginning with the creation, leading to a consummation in the future, and justifying the ways of God to man.
• II. The existence of a small section of mankind whom God specially loves. For Jews, this section was the Chosen People; for
Christians, the elect.
• III. A new conception of ‘righteousness’. The virtue of almsgiving, for example, was taken over by Christianity from later Judaism. The importance attached to baptism might be derived from Orphism or from oriental pagan mystery religions, but practical philanthropy, as an element in the Christian conception of virtue, seems to have come from the Jews.
• IV. The Law. Christians kept part of the Hebrew Law, for instance the decalogue, while they rejected its ceremonial and ritual parts. But in practice they attached to the Creed much the same feelings that the Jews attached to the Law. This involved the doctrine that correct belief is at least as important as virtuous action, a doctrine which is essentially Hellenic. What is Jewish in origin is the exclusiveness of the elect.
• V. The Messiah. The Jews believed that the Messiah would bring them temporal prosperity, and victory over their enemies here on earth; moreover, he remained in the future. For Christians, the Messiah was the historical Jesus, who was also identified with the Logos of Greek philosophy; and it was not on earth, but in heaven, that the Messiah was to enable his followers to triumph over their enemies.
• VI. The Kingdom of Heaven. Other-worldliness is a conception which Jews and Christians, in a sense, share with later Platonism, but it takes, with them, a much more concrete form than with Greek philosophers. The Greek doctrine — which is to be found in much Christian philosophy, but not in popular Christianity — was that the sensible world, in space and time, is an illusion, and that, by intellectual and moral discipline, a man can learn to live in the eternal world, which alone is real. The Jewish and Christian doctrine, on the other hand, conceived the Other World as not metaphysically different from this world, but as in the future, when the virtuous would enjoy everlasting bliss and the wicked would suffer everlasting torment. This belief embodied revenge psychology, and was intelligible to all and sundry, as the doctrines of Greek philosophers were not.
To understand the origin of these beliefs, we must take account of certain facts in Jewish history, to which we will now turn our attention ...“
— Bertrand Russell, A History of Western Philosophy (1945), Book Two. Catholic Philosophy, Part. I. The Fathers, Ch. I: The Religious Development of the Jews, pp. 307-09
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* Orphism (more rarely Orphicism; Ancient Greek: Ὀρφικά, romanized: Orphiká) is the name given to a set of religious beliefs and practices originating in the ancient Greek and Hellenistic world, associated with literature ascribed to the mythical poet Orpheus, who descended into the Greek underworld and returned.