Why didn’t you lie?
In Genesis 20 Abraham lies concerning Sarah, his wife, when they travel through Gerar to live in the land of King Abimelech. In Genesis 26, Isaac, when confronted with a famine in the land, goes down to dwell in Gerar, and he, like his father, lies to King Abimelech concerning Rebeccah, his wife, likewise saying that she is his sister.
So when Jacob sends his sons down to Egypt when there is a famine in the land of Canaan, and they return with the news that the ruler of the land (Joseph) has accused them of being spies and are required to bring their youngest brother to him. It should not come as too great of a surprise that part of Jacob’s response is the question: “Why did you deal so wrongfully with me as to tell the man whether you had still another brother?” That is, ‘Why didn’t you lie?’ Why were you so free with information about your family? The family custom seems to have been protection of family through deception. Of course these deceptions were always found out, but they always resulted in great blessing for Abraham and Isaac.
The concern of Abraham and Isaac had been for their wives, that the ruler of the land (Abimelech) would take them. Now the ruler of Egypt has demanded that the youngest son of Jacob be brought to him to prove their innocence. The tables have been turned. Perhaps Joseph knew these customs of his family and for this reason asked very pointed questions, as the brothers relate that he did (Gen. 43:7). Notice now, it is Joseph who is doing the deceiving. He is the righteous deceiver, but his family well receive great blessing nevertheless.