מדרש על בראשית 20:17

(Lev. 7:11:) “This is the law of the sacrifice for peace offerings.” This text is related (to Prov. 3:17), “The ways [of wisdom] are ways of pleasantness, and all her paths are peace.” Whatever is written in the Torah is written to [establish] peace. Although wars are written about in the Torah, they are written about for the sake of peace. You find that the Holy One, blessed be He, cancelled the decree [of utter destruction (herem)] for the sake of peace. When? When the Holy One, blessed be He, said to Moses (in Deut. 20:19), “When you besiege a city a long time.” Now concerning that whole matter, the Holy One, blessed be He, had said that he should destroy them, as stated (above in vs. 17), “No, you shall utterly destroy them.” However, Moses did not do so. Rather he said, “Am I to go and smite who has sinned and who has not sinned? Instead, let me come against them in peace, as stated (in Deut. 2:26-27), “Then I sent messengers from the Desert of Kedemoth [unto King Sihon of Heshbon] with words of peace […]. I will traverse your land.” When he saw that he did not come in peace, he smote him, as stated (in Numb. 21:35), “So they smote him, his children, and all his people.” The Holy One, blessed be He, said to him, “I Myself told you (in Deut. 20:17), ‘No, you shall utterly destroy them,’ but you did not do this. By your life, just as you have said, so will I do.” Thus it is stated (in Deut. 20:10), “When you draw near unto a city to fight against it, you shall offer terms of peace unto it.” Therefore, it is so stated (in Prov. 3:17), “The ways [of wisdom] are ways of pleasantness, and all her paths are peace.”

And the Lord remembered Sarah (Gen. 21:1). Scripture states elsewhere in reference to this verse: That confirmeth the word of His servant, and performeth the counsel of His messengers. That saith of Jerusalem: “She shall be inhabited”; and of the cities of Judah: “They shall be built” (Isa. 44:26). That confirmeth the word of His servant refers to Abraham, for the Holy One, blessed be He, said: I opened his womb (Abimelech) on account of Abraham, My servant, who prayed in his behalf, as it is said: And Abraham prayed unto God (Gen. 20:17). Performeth the counsel of His messengers alludes to the angels who informed Abraham that he would have an offspring, as it is said: I will certainly return unto you when the season cometh around (ibid. 18:10).

That saith of Jerusalem: “She shall be inhabited”; and of the cities of Judah; “They shall be built” relates to the subject we are discussing. Though the nations were confident that Jerusalem would not be rebuilt, it will be rebuilt, as it is said: That saith of Jerusalem: “She shall be inhabited”, and it is written elsewhere: When the Lord hath built Zion (Ps. 102:17). But if you are doubtful as to the ultimate rebuilding of Jerusalem, look unto Abraham, your father, and unto Sarah who bore you (Isa. 51:2), for just as I did in behalf of Sarah and Abraham, so I shall do in behalf of Jerusalem.