We understand why “tzadikim” is written chaseir in Hashem’s response, but why does it appear that way in the entire parsha, even in Avraham’s pleading?
The gemara (Ta’anis 21b) writes that there was once a plague that affected all the towns except for that of Rav. The townsfolk had a dream in which it was revealed that the miracle of the town being spared was not due to Rav’s merit, but rather due to a certain person who would lend out shovels to help in burial. The gemara says further that there was a fire that harmed a bunch of towns except for that of R’ Huna. Again, the townsfolk had a dream in which it was revealed that the town was not spared in Rav Huna’s merit, but rather in the merit of a certain lady who would light the stove in the morning from which her neighbors then lit their own fires.
The Maharasha asks: isn’t bichlal masayim manah? If the merit of small acts of kindness was enough to save these towns, they certainly would have been spared in Rav or Rav Huna’s merit! Why do Chazal seem to go out of their way not only to credit the little people, but also to stress that it was not Rav or Rav Huna’s merit that caused the miracle?
The Sefas Emes on that gemara has an incredible hesber. We know that sometimes punishment can be so harsh that it strikes indiscriminately at both tzadikim and reshaim. “Keivan she’nitan reshus l’mashchis aino mavchin…” – once the power of destruction is unleashed, anyone in its path gets harmed, even tzadikim. There is, however, an exception for what I am going to call super tzadikim. These righteous-of-the-righteous are so outside the bounds of reality that even when the mashchis is on the prowl, even when destruction is wreaking havoc on all, they are spared. The upside is clear, but there is also a downside. Because these super-tzadikim stand as individuals outside of any relation to what is happening around them, their zechuyos cannot help spare anyone other than themselves.
Rav and Rav Huna were outside the boundaries of the world; they were on a different plane than anyone else living around them. They would not be harmed by a plague or a fire, but their zechuyos would not help those who surrounded them either. Davka those smaller acts of kindness, davka tzadikim who lived on the same plane as everyone else, amidst their brethren, and still managed to still maintain a certain degree of righteousness, were the ones whose merit could be counted among the deeds of their brethren to tip the scale in favor of their all being saved.
This, writes the Sefas Emes, explains Avraham's tefilos. Avraham was not looking for super-tzadikim in Sdom – individual merit of that kind was so outside the plane of reality the rest of Sdom was living on that it would serve only to spare those isolated individuals. Avraham was looking for the little tzadikim, people whose small acts of kindness and goodness, even as they lived the same day to day struggle as their peers, made them stand out as worthy. Such people, tzadikim who were “b’toch ha’ir” (see the Meshech Chochma), were the ones whose merit might have tipped the balance in favor of the entire city being spared.