Strengthen your faith in God's word

Where did Cain's wife come from?

Before answering this, one thing must be made clear: This must be taken literally (please, brothers and sisters in the faith, understand that reading the Bible literally does not in any way destroy theological, spiritual, symbolical, moral, prophetic truth, nor are there any inconsistencies in God‘s Word) and this problem must be understood in the situation of Adam’s time, not according to how we view the world today.

Now, starting with Adam, he had Abel, Cain, and later Seth after being kicked out of the Garden of Eden. He also had sons and daughters after that.
Gen. 5:4 And the days of Adam after he had begotten Seth were eight hundred years: and he begat sons and daughters
Adam lived 800 years more after Seth was born. Adam could have had many, many children.

Notice also that Gen. 4:17 says that “Cain knew his wife”. He didn’t find her, but “knew” her, meaning he had sexual relations with her. This also implies that before making her his wife, Cain personally knew her, which is what any couple would do before marrying each other. So the question is not “where Cain’s wife came from?”, but “who was Cain’s wife?”.

From what has already been said, it is obvious that Adam’s sons married their sisters. Please, understand this:
1. There was no other option. Besides, they never would of thought it was wrong in the first place.
2. There was no one to report them to. Who would you tell? Adam and his (huge) family were practically the only humans in the world.
3. There were no laws against it at first, until about 2500 years later. Until then, the law was not needed. (Lev. 18:6-18).

Just from looking at the age of Man in Adam’s time, they lived to be nearly 1000 years. This means two things:
1. That the environment was far more different than today that people were able to live more than 900 years.
2.That humans were far better than we are today, which means that humans were genetically perfect back then. There were no genetic defects, and thus, marrying sisters were no problem at all.

If Cain marrying his sister is still a problem to you, then just look at Adam and Eve. He married essentially his rib. Now that is far more genetically similar than a brother and sister marrying each other. This practice of marrying within the family lasted all the way until Abraham, Isaac, and Jacob.
Because the world was affected by Sin at Adam’s Fall and because the Global Flood of Noah environmentally changed the world for the worse, Man’s longevity went from 900 before the Flood to 400, 200, and finally 100 after the Flood. It seems that the Genetic DNA perfection ended after the Patriarchal Fathers died. Thus, from Joseph and onwards to today, Incest (other than being a moral issue of respecting the family) has genetically been a problem to Humanity. That is one major reason why the Law forbade Incest because God knew what the consequences of Sin in the world would lead to: A deterioration of Mankind’s DNA.