And Abimelech said to Abraham: Good News Translation drops this as unnecessary in the dialogue. Abimelech continues to accuse Abraham by pursuing his questions.

What were you thinking of, that you did this thing?: thinking of is literally “What did you see,” where “see” has the sense of “foresee,” “expect,” “hope to gain.” We may translate “What did you hope to accomplish?” “What were you after?” “What did you expect to get from it?” Good News Translation “Why did you do it?” seems to omit the element of personal gain assumed in Abimelech’s question. The last part of the verse may be rendered, for example, “What did you expect to get by doing this thing?” Since “this thing” refers to saying that Sarah was his sister, it may be clearer to translate “What did you expect to get by saying that Sarah was your sister?” or “… by hiding the fact that she was your wife?”

Quoted with permission from Reyburn, William D. and Fry, Euan McG. A Handbook on Genesis. (UBS Helps for Translators). New York: UBS, 1997. For this and other handbooks for translators see here .