This was to cover Cain in the future as the human population increased.
When God first created Adam and Eve, they were very close to 'perfection', but they had many other children after Cain and Abel. The Bible doesn't mention the names of Adam's and Eve's daughters.
Genesis 3:20 says: "After this Adam called his wife's name Eve, because she had to become the mother of everyone living". Genesis 5:5--"So all the days of Adam that he lived amounted to nine hundred and thirty years and he died". Adam and Eve continued to have many children until Adam died.
So Cain married his sister or his niece, but not his mother Eve. The Bible relates that people back then married relatives, because as you pointed out there weren't that many people on the Earth. Cain was an adult when he killed Abel. Genesis 4:17says--Afterward Cain had intercourse with his wife and she became pregnant and gave birth to E′noch. Then he engaged in building a city and called the city's name by the name of his son E′noch".
Leviticus 17:6-17 was part of the Law of Moses to teach the people that they could no longer marry relatives. Birth defects were showing up, and the Messiah was to be born from among the Israelites. Why would God give them laws forbidding marrying relatives if they weren't doing this?
God put a mark on Cains cheek to protect
ANSWER #2
The punishment of Cain is found in Genesis 4:11-12.
12When you till the ground, it shall not from now on yield to you her strength; a fugitive and a vagabond shall you be in the earth. 13 And Cain said to the LORD, My punishment is greater than I can bear.
14 Behold, you have driven me out this day from the face of the earth; and from your face shall I be hid; and I shall be a fugitive and a vagabond in the earth; and it shall come to pass, that every one that finds me shall slay me. 15 And the LORD said to him, Therefore whoever slays Cain, vengeance shall be taken on him sevenfold. And the LORD set a mark on Cain,
THE MARK OF CAIN
The discription of the mark put upon Cain is found not in the King James Bible but in another ancient manuscript.
This is confirmed by the Apocalypse of Elijah http://en.wikipedia.org/wiki/Apocalypse_of_Elijah;
Chr 3 vs 14,15, "For behold I will tell you his sign so that you might know him. He is a . . (words missing) . .of a skinny-legged young lad, having a tuft of gray hair at the front of his bald head."
The word translated as "mark" in Gen. 4:15 is 'owth, which could mean a sign, an omen, a warning, or a remembrance. In the Torah, the same word is used to describe the stars as signs or omens, the rainbow as the sign of the flood (Gen. 9:12), circumcision as a token of God's covenant with Abraham, and the miracles performed by Moses before the Pharaoh. Thus, the text of the Bible only explicitly describes how the mark was to function as a sign or warning.
Below are the Bible passages from Genesis 4 (NIV translations): 6 Then the LORD said to Cain, "Why are you angry? Why is your face downcast? 7 If you do what is right, will you not be accepted? But if you do not do what is right, sin is crouching at your door; it desires to have you, but you must master it." 9 Then the LORD said to Cain, "Where is your brother Abel?"
"I don't know," he replied. "Am I my brother's keeper?" 10 The LORD said, "What have you done? Listen! Your brother's blood cries out to me from the ground. 11 Now you are under a curse and driven from the ground, which opened its mouth to receive your brother's blood from your hand. 12 When you work the ground, it will no longer yield its crops for you. You will be a restless wanderer on the earth."
In Genesis 4:6-7, God asked Cain why he was angry and told him that if he did what was right, he would be accepted. God also warned Cain about the consequences of not doing what was right.
The Bible doesn't say what it was.
God asked Cain where is your brother Abel?
Cain slew Abel out of jealousy and anger, as God favored Abel's offering over Cain's. This act of violence resulted in the first murder recorded in the Bible.
The "mark of Cain" in the Bible refers to a sign from God that was put on Cain to protect him from being killed. According to the Book of Genesis, after Cain killed his brother Abel, God placed a mark on him to warn others not to harm him. The exact nature of this mark is not specified in the Bible.
According to the Bible, God punished Cain for killing his brother Abel by making him a wanderer on the earth. God also put a mark on Cain to protect him from anyone who might try to harm him, stating that "whoever kills Cain will suffer vengeance seven times over."
Cain and Abel are famous because they were two brothers in the Bible who were involved in the first recorded murder, where Cain killed Abel out of jealousy. Their story is a significant part of the Judeo-Christian tradition and has been retold in various cultural and religious contexts.
Abel owed God money.
God asked Cain where is your brother Abel?
God wanted to see whether or not Cain would be willing to address the problems concerning his bad intentions when providing his sacrifice. Cain showed that he was disinterested.
The duration of And God Said to Cain is 1.82 hours.
Cain. See Genesis 4:6.
And God Said to Cain was created on 1970-02-05.
God set a mark on Cain because God had mercy on Cain. After pronouncing Cain's punishment, and hearing Cain's reply - "My punishment is more than I can bear.", God put a mark on Cain - Genesis 4.15. And the LORD said unto him, Therefore whosoever slayeth Cain, vengeance shall be taken on him sevenfold. And the LORD set a mark upon Cain, lest any finding him should kill him.
Cain. KJV
He decreed that if anyone were to slay Cain, God would judge him seven times more than he had Cain.
Short answer - God probably had divine love for Cain, but that doesn't mean God "liked" Cain's actions and choices. Cain decided to openly rebel against God. Cain's rebellion toward God wasn't temporary, it was a permanent condition of his heart. In effect, Cain alienated himself from God's Favor and Love. Remember, Cain was "cursed" only after he refused to repent and change his relationship for the better with God.
Cain. Cain was jealous of his brother. And didn't ask God for forgiveness. God also said "One child will fall into my hands, fall into peace, love and happiness. And one will fall into Satan's hands, fall into hatred, sin, and temptation".
God put a mark on Cain but the Bible does not say where or what type of mark God put on him.