Avraham made a covenant between himself and Avimelech and between their respective descendents. Many commentators wonder why Avraham would agree to this, with the Rashbam going as far as to say that the trial of akeidat Yitzchak was a punishment for this unauthorized treaty. We will try to suggest a new idea, but only after raising another issue. This same Avimelech was the one who had taken Sarah into his palace, with the hope of a marriage under pressure. This seems to be a repeat of the sins of the generations before the flood, in which the "sons of the powerful" took for themselves wives as they desired (see Bereishit 6:2 and Rashi ad loc.). As we discussed in the last few weeks, the covenant of mankind with Hashem after the flood should preclude this. What saving graces did Avimelech have that made him worthy of Avraham’s cooperation?
If we compare the Torah’s account of the taking of Sarah by Avimelech with that done by Paroh, we will find nuanced but important differences between the two. Regarding Paroh, after undergoing serious plagues in his household and uncovering that Sarah was the cause (the Torah does not say how he knew), Paroh registered a quick complaint against Avraham and sent him away (ibid. 12:14-20). He was not interested in explaining his own actions or salvaging the relationship with Avraham.
Avimelech’s story is quite different. Firstly, the Torah writes explicitly that Hashem appeared to him in a dream to inform him of his pending sin of taking Sarah, instead of his receiving great afflictions. Avimelech even responded to Hashem that he was innocent, and Hashem partially accepted his excuse. Avimelech took responsibility for his actions. The next morning, he called his servants together to brief them, and they all feared Hashem. When he complained to Avraham for calling Sarah his sister, Avraham felt a need to explain his own actions. Furthermore, Avimelech accepted Avraham’s special spiritual status and invited him to stay in the region as an honored guest. Avraham decided that, indeed, it was more worth his while to live in Avimelech’s Philistine region of the Land than to return to the Cana’anite region (ibid. 21:34, see Rashi ad loc.).
Apparently these were among the differences that convinced Avraham that there was enough positive about Avimelech and his people to accept his overture of good will. In our days, as well, it is worthwhile to give a good look at potential partners and see if they are of the moral standing to deserve our trust and cooperation.