Genesis 5:4 And the days of Adam after he had begotten Seth were eight hundred years: and he begat sons and daughters:
One of the favorite questions of the skeptic is; where did Cain get his wife? In this verse you see that Adam and Eve had other sons and daughters. We do not know their names. We do not get their stories but they were there.
That is where Cain got his wife. He married his sister. That wasn’t unusual in Bible or historic times. Abraham was married to his half sister. There are other stories of familial marriages. Abraham sent his servant back to his people to get a wife for Isaac. He marries his first cousin.
God only puts the stories in the Bible that we need to know His story! He is telling us the story of redemption, of salvation. There is no wondering if we have all the facts. We do not!
God chooses the stories that He needs to teach us the lessons that we need. If not there would be no way that 4,000 years of history could be contained in so few pages as the Bible. Remember there is there the history of Israel, the story of Christ, and the history of the early church. Much is left out!
Why? Because He tells us what we need to know to get the point He is getting across. We are sinners. Men always fail. God is always good. Salvation comes through Jesus Christ!