Sometime later, there was a terrible famine in the land of Cana’an (later to be known as Eretz Yisrael, the land of Israel), and the people had very little food to eat.
Yitzchak thought he should go down to Egypt as his father Avraham had done in a similar situation. However, HaShem told him, “Do not go. You were brought upon the altar as a sacrifice. You are indeed too holy to leave Eretz Yisrael. Stay here and I will protect you. I will bless you with offspring, as many as the stars in heaven. I will give you this land, just as I promised your father Avraham.”
Yitzchak stayed in Cana’an and settled in the city of Gerar, the capital city of the Plishtim (Philistines).
The Plishtim asked Yitzchak, “Who is that lovely lady with you?”
Yitzchak didn’t want to reveal that Rivkah was his wife. Rivkah was very beautiful and he was afraid that the Plishtim would kill him, so that she could marry King Avimelech.
Yitzchak replied, “This woman here is… my…my sister.”
All the kings in the land of the Plishtim were given the title “Avimelech,” just as the Egyptian kings were called “Pharaoh,” the kings of Amalek “Agag,” and the Roman kings “Caesar.”
BTW: In Iran, the king was known as “Shah” (no need to be quiet about that.) In many Arab countries, kings were called “Sultan.” In India, it’s “Maharajah.” And in old Russia, the king was called “Czar.”
Get the idea?
At times, in order to save a life, it is permissible to stray from the truth. Yitzchak was in danger of being killed, so he told the Plishtim that Rivkah was his sister.