WHERE DID CAIN GET HIS WIFE?
Non-Christians often trip up Christians when they ask where Cain got his wife. If one is to believe in the inspiration of Scripture, Christians must be able to answer this question.
And Cain went out from the presence of the LORD, and dwelt in the land of Nod, on the east of Eden. And Cain knew his wife; and she conceived, and bare Enoch: and he builded a city, and called the name of the city, after the name of his son, Enoch. (Genesis 4:16-17)
And Adam lived an hundred and thirty years, and begat a son in his own likeness, after his image; and called his name Seth: And the days of Adam after he had begotten Seth were eight hundred years: and he begat sons and daughters: (Genesis 5:3-4) [emphasis mine]
And Seth lived an hundred and five years, and begat Enos: And Seth lived after he begat Enos eight hundred and seven years, and begat sons and daughters: (Genesis 5:6-7) [emphasis mine]
Most likely, Cain's wife was one of his sisters, as Adam also had daughters, as stated in Genesis 5:3-4. Less likely, she was one of his nieces, as Seth at least also had daughters, as stated in Genesis 5:6-7. What about not marrying close relatives? God did not give this law until the time of Moses, thousands of years later, as shown below in Leviticus 18:6-18:
None of you shall approach to any that is near of kin to him, to uncover their nakedness: I am the LORD. The nakedness of thy father, or the nakedness of thy mother, shalt thou not uncover: she is thy mother; thou shalt not uncover her nakedness. The nakedness of thy father's wife shalt thou not uncover: it is thy father's nakedness. The nakedness of thy sister, the daughter of thy father, or daughter of thy mother, whether she be born at home, or born abroad, even their nakedness thou shalt not uncover. The nakedness of thy son's daughter, or of thy daughter's daughter, even their nakedness thou shalt not uncover: for theirs is thine own nakedness. The nakedness of thy father's wife's daughter, begotten of thy father, she is thy sister, thou shalt not uncover her nakedness. Thou shalt not uncover the nakedness of thy father's sister: she is thy father's near kinswoman. Thou shalt not uncover the nakedness of thy mother's sister: for she is thy mother's near kinswoman. Thou shalt not uncover the nakedness of thy father's brother, thou shalt not approach to his wife: she is thine aunt. Thou shalt not uncover the nakedness of thy daughter in law: she is thy son's wife; thou shalt not uncover her nakedness. Thou shalt not uncover the nakedness of thy brother's wife: it is thy brother's nakedness. Thou shalt not uncover the nakedness of a woman and her daughter, neither shalt thou take her son's daughter, or her daughter's daughter, to uncover her nakedness; for they are her near kinswomen: it is wickedness. Neither shalt thou take a wife to her sister, to vex her, to uncover her nakedness, beside the other in her life time. (Leviticus 18:6-18)
 All scripture references are from the King James Version unless otherwise noted. Please see my about page for why I chose this translation.