This paper compares Masoretic Text(MT), LXX, and Jubilees, which are considered canonical by the Ethiopian Orthodox Tewahedo Church, with regard to the post-flood genealogy of Shem in Genesis 11. We examines the genealogy of Shem after the flood, focusing on the figure of Cainan, who is mentioned in LXX Genesis 10:24; 11:12-13 and in Jubilees 8:1-4, and confirms the correlation between exogamy and idolatry. Cainan, the 13th generation, introduced astrology in the line of Shem and idolaters appeared in succession thereafter. Endogamy, however, is not synonymous with maintaining the purity of Yahweh worship, and, while a person marries outside a community, exogamy does not directly cause idolatry. However, it seems that within the religious context of specific societies, exogamy and idolatry are mutually influencing factors. In the case of Cainan and his descendants, exogamy appears from the 15th generation, heathens eventually appear from the 16th generation, Peleg, to the 20th generation, Terah.
Due to the exogamy initiated by Cainan, the purity of the bloodline within the line of Shem gradually degraded, and along with exogamy, astrology and idolatry appeared within the line of Shem. Terah’s early life was marked by idolatry, but his conversion to monotheism is revealed in his blessing of his son Abram as he prepares to go to the land of Canaan. In contrast to previous generations who worshipped idols, Abram was the one who reinstituted the faith of Yahweh to the line of Shem, and also restored the endogamy through his marriage to Sarai. I hope that this paper can serve as an exhortation to the Korean Old Testament academic community that the study of the Book of Jubilees is also necessary to expand the horizon of Old Testament studies.