"Where did Cain get his wife?" might be the most asked question unbelievers use when challenging the authenticity of the Bible. Those who bother answering it, do so using logic and not Scripture; the Bible does not say. Some suggest that God provided Cain with a wife the same way He did for Adam, but they are wrong. Genesis 3:20 says that Eve "was the mother of all living." Again, a little logic is needed to explain why she was not the mother of Adam, of animals, and of plants (those wanting to reject God's Word seem desperate at times). Cain either had to marry a sister, or he had to marry the offspring of the union of a brother and sister (Gen. 5:4). Either way, the questioner usually responds, "Yuk!"
Another question that even believers ask is, "Why didn't God accept the sacrifice of Cain?" Again, the answer requires logic. Ironically, it is logic that produces the question itself. If Cain was a farmer and Abel was a shepherd, and if Abel offered the best he had, a fat firstling, what was so wrong with Cain bringing "the fruit of the ground"? Some postulate that because God had sacrificed animals to provide clothing for Adam and Eve, He had given them instructions on making offerings; the Word does not say that. Others suggest that God knew the heart of Cain "was not in it," or that the "veggies" were not the first fruit or the best that he had to offer; again, the Word is silent. However, there are some clues. 1 John 3:12 tells us that Cain's works were evil but that Abel's were righteous. There are two kinds of evil works or sin: failing to do the right thing, or doing doubtful things (Jam. 4:17; Rom. 14:23). If Cain's offering was done knowing God wanted something else, it was sin. If Cain did not offer his sacrifice in faith, it was sin. Notice that Abel's sacrifice was offered "by faith." Perhaps Cain was logical, and Abel was faithful.
There may be some connection with the family of Isaac, but it is really a stretch. Isaac had two sons; one was a man who produced meat by hunting, and the other appears to have been a cook who had made vegetable soup (Gen. 25:27-30). Isaac was pleased with the offering of venison, but didn't seem to be too fond of soup. To accept this theory, two assumptions would have to be made: God eats the sacrifices man offers, and His appetite changed later when He required offerings of bread, mutton, and wine (Lev. 23:12-13). But I digress.
There are actually more questions about Cain than there are Bible verses which speak of him. Other than Genesis Four, there are only three verses that refer to him (Heb. 11:4; 1 Jn. 3:12; Jude 1:11). Other unanswered questions are: "What was the mark God put on him for protection?" "Why was there a name for the land Cain settled in?" "Why did Cain build a city when he was a farmer?" "From where did the large number of people come that required a city?" And one that I would like to ask, "Why did God allow the first person raptured to be named after Cain's first son (Gen. 4:16 w/ 5:18-24)?" I would like to say, "Tune in tomorrow for the answers," but I haven't got a clue. Lord willing, I will continue discussing the "first family."