Or HaChaim on Genesis 26:29/אור החיים על בראשית כ״ו:כ״ט

1 אם תעשה עמנו, "if you will do with us, etc." They were careful to include in the wording of the covenant that it was in recognition of favours they had done to Isaac, whereas they referred to the eventuality that Isaac might reciprocate by doing harm to them. This is the reason that the whole verse is worded so unusually, as if it had been interrupted in the middle. The words "if you will do evil with us" should by rights have been part of the previous verse, providing the rationale for Avimelech seeking this agreement.

2When you keep in mind what we have said, it becomes clear that the words are in their proper place, however. Avimelech and company stressed that just as they had not done any harm to Isaac in the past they now expected him to swear that he in turn would not do something that would harm them in the future. Isaac could not be expected to understand what they meant by the טוב, the good they had done for him, until they explained that the very fact that they let him depart whole in body and assets was in itself an act of kindness. Kings, i.e. governments, sometimes pass legislation to extend financial aid to some of their subjects. They do so for one of two reasons. 1) If the day would come when the government is in need of financial aid they would have wealthy citizens to call upon to provide loans to the government. 2) In order to enhance the economic standing of their countries. A country which contains many wealthy people thereby adds to the glory of its rulers. As a result one could have argued that any favours Avimelech had done for Isaac were not of an altruistic nature but were designed to enhance the king's personal reputation as a ruler over a successful country. Avimelech denied such an interpretation of his motives by saying: "just as we never harmed you," meaning that there were no selfish motives in that part of the טוב they had done for Isaac. The very fact they had let Isaac depart with all his assets intact [and had not imposed an emigration tax Ed.] had made Avimelech's country poorer. According to their reasoning this proved that every kindness they had shown Isaac had been genuine, not self-interest. All of this was alluded to in the words ראו ראינו.

3[At this point the author quotes a line he saw in Bereshit Rabbah according to which Avimelech's words are proof that the Philistines did not do Isaac any true favours. He finds this difficult and deals with it. Since I have not found such a line in my edition of Bereshit Rabbah, I have omitted this paragraph. Ed.]

4אתה עתה ברוך ה', "you are now the one who is blessed by the Lord." They had come to this realisation when they saw that Isaac continued to prosper in spite of having been expelled from their midst. Seeing that Isaac had not been deprived of any of the favours they used to bestow on him as a result of their having expelled him, he had no reason not to render the oath they requested from him as a quid pro quo.

5The author argues that in spite of the definition of the Rivash that what constitutes an oath which is rendered as a quid pro quo is the favour which is rendered at the time of the oath, the same holds true if the oath was sworn in recognition of favours received previously.

6Avimelech also wanted to explain with this statement why they did not invite Isaac to return to Gerar. Seeing that after leaving Gerar Isaac had prospered even more than while he had been there, there was no point to invite him to come back there. Previously it could have been argued that he was the beneficiary of the help of G'd extended by means of intermediaries such as the local government in Gerar, i.e. Avimelech himself. Now that he lived in no-man's land it was clear that his success was due entirely to G'd's direct help.

7Avimelech also wanted to deny the argument that they had caused Isaac's good fortune to be interrupted by their expulsion; this could not have been the case seeing that G'd had been its author. The fact that he was still better off today than when he resided amongst them was the proof; עתה ברוך ה', "now that they had already done all that was in their power with the means at their disposal, it was clear that he was blessed by the Lord" since he had found the real source of such blessing. All these arguments were designed to elicit an oath the legality of which would be unassailable under any circumstances. There is a discussion in Gittin 46 why the Jewish people did not make war against the Gibeonites when they found out that the latter had tricked them into a promise to treat them as allies instead of as Canaanites (Joshua 9,18). Rabbi Yehudah holds that since the oath was sworn by the leaders of the Jewish people, Israel could not take action denying the validity of that oath. The other rabbis disagree, claiming that the Israelites' undertaking was never valid as it had been based on the Gibeonites' declaration that they were a people who lived far from the land of Canaan. Clearly, Rabbi Yehudah was concerned with the image of Jewish leaders who by defaulting on an undertaking denigrate the reputation of G'd whom they represent. Rashi explains that Rabbi Yehudah's point is not that the oath was valid, but that the Gentiles must not be allowed to say that Jewish leaders were guilty of perjury. We must remember that Rabbi Yehudah's point is not a legal one, i.e. a Mosaic law, but an act of piety that Jewish leaders have to impose upon themselves. Besides, even according to Rabbi Yehudah, such a consideration is in place only when the oath was as public as that of the Jewish people to the Gibeonites. Oaths between a relatively small group of people such as Isaac and Avimelech's entourage would certainly not fall under that heading.

8Furthermore, an additional reason why the other rabbis disagreed with Rabbi Yehudah is that the Gentiles are well aware of the mechanics and the conditions when oaths are subject to annulment. This being so, the question of חלול השם, public desecration of G'd's name which troubled Rabbi Yehudah did not even arise.