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.
Judaism
Countries such as the United States, Israel, Canada, United Kingdom, Argentina and South Africa contain large Jewish populations. Jewish religious practice varies widely through all levels of observance. According to the 2001 edition of the National Jewish Population Survey, in the United States' Jewish community—the world's second largest—4.3 million Jews out of 5.1 million had some sort of connection to the religion. Of that population of connected Jews, 80% participated in some sort of Jewish religious observance, but only 48% belonged to a congregation, and fewer than 16% attend regularly.