The mythos, the raison d'tre, of Christianity is to provide all human beings with the only valid path to salvation. Christians believe people are by nature sinful. Christians believe that Jesus was both the Son of God and God the Son, God made incarnate; that Jesus' death by crucifixion was a sacrifice to atone for all humanity's sins, and that acceptance of Jesus as the Christ saves one from sin. Judaism's raison d'tre is to give concrete form to the covenant between God and the Jewish people. The Torah (teaching) tells the story of this covenant, and provides Jews with the terms of the covenant. The Torah thus guides Jews to walk in God's ways, to help them learn how to live a holy life on earth, and to bring holiness into the world and into every part of life so that life may be elevated to a high level of sanctity. Judaism does not see the afterlife as a core part of this, or a major factor needed to justify why it is necessary. Ideally a faithful life and good deeds should be ends in themselves, not means (Lodahl 57-98).
As for the concepts of God, it should be said that both Jews and Christians believe in the God of Abraham, Isaac and Jacob, for Jews the God of the Tanakh, for Christians the God of the Old Testament, the creator of the universe. Both religions agree that God shares both transcendent and immanent qualities. How these religions resolve this issue is where the religions differ. Most of Christianity posits that God is the Trinity; in this view God exists as three distinct entities which share a single divine essence, or substance. In those three there is one, and in that one there are three; the one God is indivisible, while the three entities are distinct and unconfused: Abba God, Jesus and the Holy Spirit. It teaches that God became especially immanent in physical form through the Incarnation of Jesus, who is believed to be at once fully God and fully human. By contrast, Judaism sees God as a single entity, and views trinitarianism as both incomprehensible and a violation of the Bible's teaching that God is one. It rejects the notion that Jesus or any other object or living being could be "God", that God could have a literal "son" in physical form or is divisible in any way, or that God could be made to be joined to the material world in such fashion. Judaism does not believe that God requires the sacrifice of any human. This is emphasized in medieval Jewish traditions concerning the story of the Akedah, the binding of Isaac. In the Jewish explanation, this is a story whereby God wanted to test Abraham's faith and willingness, and Isaac was never going to be actually sacrificed. Thus, Judaism rejects the notion that anyone can or should die for anyone else's sin (Levenson 48-53).
Understanding of the Bible. Jews and Christians seek authority from many of the same basic books, but they conceive of these books in significantly different ways. The Hebrew Bible is comprised of three parts: Torah (the five books of Moses), Nevi'im (the writings of the Prophets), and Ketuvim (other writings canonised over time, such as the Books of Esther, Jonah, Ruth or Job). Collectively, these are known as the Tanakh, a Hebrew acronym for the first letters of each. Rabbinical Judaism traditionally believes that these written works were also accompanied by an oral tradition which taught