Another interpretation of "Far be it from You" (Genesis 18:25): Abraham said: Master of the Universe, I foresee by the Holy Spirit that a certain woman is destined to save an entire city; am I then not worthy to save these five cities? And who is that woman? She is Serah bat Asher. At the time when Sheba ben Bichri rebelled against David and came to Abel, as it is said, "[and they came and besieged him in Abel,] and all the people who were with Joab were battering the wall to bring it down" (2 Samuel 20:15). When Serah perceived the matter, she began to cry out: Call Joab to me. When Joab came, she said, "Are you Joab?" And he said, "I am" (2 Samuel 20:17). She said: Are you that wise one whom Scripture praises, "he who sits in the seat of wisdom" (2 Samuel 23:8)? Have you not read in the Torah, "When you draw near to a city [to fight against it, you shall offer it terms of peace]" (Deuteronomy 20:10)? It was not right for you to act thus. "They used to speak in former times, saying, Let them but ask counsel at Abel" (2 Samuel 20:18), "and you shall call out to it for peace" (Deuteronomy 20:10) — at Abel; and so they concluded the matter. "Why would you swallow up the inheritance of the LORD?" (2 Samuel 20:19).
When he heard this, he became afraid, and Joab said: There is a need here, as it is said, "[Then Joab answered and said, Far be it,] far be it from me [that I should swallow up or destroy]" (2 Samuel 20:20). And you, who are merciful — is it pleasing to You to destroy these? Far be it from You to do such a thing (Genesis 18:25). And what did Joab say to her? "The matter is not so; but a man of the hill country of Ephraim, Sheba ben Bichri by name, [has lifted up his hand against the king, against David]" (2 Samuel 20:21) — a blemished man, a worshipper of idols; and there he is called a worthless man: "and his name was Sheba ben Bichri" (2 Samuel 20:1). She said to him, "I am of the peaceable and faithful in Israel" (2 Samuel 20:19) — I am the one who completed the count of Israel, as it is said, "and the name of Asher's daughter was Serah" (Numbers 26:46). Only stand in your place, and I will make peace, as it is said, "Behold, his head shall be thrown to you over the wall" (2 Samuel 20:21). And so she was confident in herself that she would give his head to Joab.
But see what she did: "Then the woman went to all the people in her wisdom" (2 Samuel 20:22). What is "in her wisdom"? She said to them: Know that Joab and all Israel are standing outside to kill us, and our sons, and our daughters. They said to her: Why? She said to them: He seeks to take a hundred men and depart. They said to her: Let him take two hundred. She said to them: He seeks only fifty men. They said to her: Let him take a hundred. She said to them: He seeks only five. They said to her: Let him take ten. She said to them: He seeks only one, Sheba ben Bichri by name. As soon as they heard this, they went and cut off his head, as it is said, "and they cut off the head of Sheba ben Bichri" (2 Samuel 20:22).
See the wisdom of this woman! Just as Abraham came with wisdom before the Holy One, blessed be He, coming down from fifty to forty, and from forty to thirty, and from thirty to twenty, and from twenty to ten, so too did she. "Then the woman went to all the people in her wisdom" — concerning her Solomon gives praise: "Wisdom is better than weapons of war" (Ecclesiastes 9:18). The wisdom of Serah was better than the weapons of war that were in Joab's hand. As soon as Joab took the head of Sheba ben Bichri, he immediately turned back and did not touch the city. Abraham said before the Holy One, blessed be He: Master of the Universe, if Joab, who took the head of one man who was guilty, spared the whole city, then You, who are merciful — would You destroy them all? Far be it from You! (Genesis 18:25).