Judaism
Christianity was originally a sect of Second Temple Judaism, but the two religions diverged in the first century. The differences between Christianity and Judaism originally centered on whether Jesus was the Jewish Messiah but eventually became irreconcilable. Major differences between the two faiths include the nature of the Messiah, of atonement and sin, the status of God's commandments to Israel, and perhaps most significantly of the nature of God himself. Due to these differences, Judaism traditionally regards Christianity as Shituf or worship of the God of Israel which is not monotheistic. Christianity has traditionally regarded Judaism as obsolete with the invention of Christianity and Jews as a people replaced by the Church, though a Christian belief in dual-covenant theology emerged as a phenomenon following Christian reflection on how their theology influenced the Nazi Holocaust.
Orthodox Judaism
In the State of Israel, where the total Jewish population is about 6.5 million, 22% of all Jewish respondents to a 2016 PEW survey declared themselves as observant Orthodox (9% "Haredim", or "Ultra-Orthodox", 13% "Datiim", "religious"). 29% described themselves as "traditional", a label largely implying little observance, but identification with Orthodoxy. The second largest Orthodox concentration is in the United States, where a 2013 PEW survey found that 10% of respondents identify as such, in a total Jewish population of at least 5.5 million. 3% were Modern Orthodox, 6% were Ultra-Orthodox, and 1% were "other" (Sephardic, liberal Orthodox, etc.) In Britain, of 79,597 households with at least one Jewish member that held synagogue membership in 2016, 66% affiliated with Orthodox synagogues: 53% in "centrist Orthodox", where congregants are often lax in observance, and 13% in "strictly Orthodox" (further 3% were Sephardi, which technically eschews the title "Orthodox").