Rashi comments: A ben sorer u’moreh, wayward and rebellious son, is put to death due to his end. The Torah foresaw the culmination of his way of thinking. He will eventually exhaust his father’s money, and, in order to maintain his habit, will be compelled to steal. A time will come when stealing will not come easily. At this point, he will resort to murder. Chazal teach: Let him die as an innocent person (before he kills someone) and not die as a guilty person. This refers to an inconsistency in a prior episode in the Torah, when the infant Yishmael was dying of thirst (after he and his mother, Hagar, had been banished from Avraham Avinu’s home). Hashem listened to Yishmael’s cries and provided him with life-sustaining water. The Ministering Angels questioned Hashem: “He, whose descendants will kill Your children with thirst – You are providing him with water?” (When the Jewish People were exiled to Babylon, they asked the Babylonians to lead them by way of Yishmael’s lands, so that they might obtain some food and drink. The Yishmaelim, true to their cruel heritage, brought out salty foods which parched the Jew’s throats. Then they refused them water, causing many of them to perish.) Hashem replied that a person is judged by his present actions – not by what he (or his descendants) might do. Why are Yishmael’s circumstances different from those of the ben sorer u’moreh, who also presently had done nothing to warrant the death penalty?
The simple explanation offered by the Mizrachi is that, at the moment, Yishmael was an innocent infant who had done absolutely nothing, unlike the ben sorer, who has already demonstrated his evil tendencies. In his own inimitable manner, each of the various commentators offer his explanation to distinguish between Yishmael and the ben sorer u’moreh.
Horav Aryeh Leib Heyman, zl, offers a novel explanation which sheds light on the Ministering Angels’ question. If one were to look closely at the text of their question (quoted in Rosh Hashanah 16b), their question focuses on the middah k’neged middah, measure for measure, aspect of sparing Yishmael. Their question was concerning the method of saving Yishmael: life-sustaining water when his descendants would cause death to the Jewish exiles through the medium of thirst. Why save him using the exact tool that his descendants would use to kill Jews?
In conclusion: The Angels were not as concerned about sparing Yishmael (because, after all, he had presently done nothing). They felt, however, that the water was one avenue of rescue that should not be employed to save him. We have a principle of middah k’neged middah, which appears to be overlooked vis-à-vis Yishmael. Hashem replied that the rule of Baasher hu sham, “As he is presently,” does not follow the rule of measure for measure. As long as Yishmael was not presently guilty of any transgression, he warranted to be saved – regardless of the method, even if it was the same measure which his offspring would use to harm Klal Yisrael.