1/21 Genesis 20:6
6 Then God said to him in the dream, "Yes, I know that you have done this in the integrity of your heart, and it was I who kept you from sinning against me. Therefore I did not let you touch her.
Abraham did it again. Fearing for his life, he instructed Sarah to say she was his sister. Once again a king, this time Abimelech, takes her to his harem. By taking a relative of a foreign tribal leader for his wife, a king would make alliances with other tribes. God came to him in a dream and warned him that he would die if he touched her. God knew that Abimelech did not know she was Abraham's wife.
Abimelech feared God and immediately returned Sarah to Abraham. He also gave Abraham animals and silver. Abraham's excuse was that he did not think the king feared God. Instead, it was Abraham who did not trust God.
Many cultures today indeed have no fear of committing adultery. Notice that God said to touch her would be a sin against Him. Also notice that since the king was unaware she was married, it was God who kept him from touching her. Adultery is a serious matter to God. He does intervene when we are ignorant. He does punish and bring consequences for sin when we violate a marriage.
Abraham seems to profit from his sin, but that is never so. An increase in wealth is not always a sign of blessing. His testimony for all the ages bears this scar; he risked his wife to save his life. The Bible is faithful to show us the flaws even in its heroes.
Consider: Adultery is a sin against God. Because marriage is a picture of our relationship with God, we must guard our hearts against excuses we would make to compromise the sanctity of our marriage. God deals with the adulterer.