At the end of our parasha, we find the first war that Bnei Yisrael fought, against Amalek, which became the symbol of the enemy that tries in every generation to destroy us. The command given to Yehoshua to fight them (Shemot 17:9) does not necessarily look any different than that of any other mandatory war. However, there is a unclear declaration made at the battle’s aftermath: "For the hand is on the seat of Hashem, a war for Hashem against Amalek in every generation" (ibid.:16).
More than 400 years later, King Shaul was commanded by Shmuel to destroy Amalek without mercy, from man to woman to child to animal of every type that belonged to them (Shmuel I, 15:3). This commandment shook Shaul, whose humanistic emotions held him back from fulfilling this task fully, causing his loss of the kingship. The gemara (Yoma 22b) says that Shaul had halachic/logical questions against the charge. He said that the Torah has a whole procedure (egla arufa) to deal with the death of a single individual, and one can only imagine what the level of concern should be regarding so many killed. Secondly, he asked, if the adult people had sinned, what could one say about the children and the animals? A voice from the heaven called out: "Do not be overly righteous!"
One can ask whether the command Shaul received, including killing even the animals, was part of the ongoing mitzva to erase the memory of Amalek or whether he was presented with a unique temporary obligation. The matter appears to depend on three opinions regarding the oath that Hashem made in regard to Amalek, as found in the Mechilta D’Rabbi Yishmael (Beshalach 2). Rav Yehoshua said that it is something that Hashem will see to when His Kingdom will be complete. Rav Elazar Hamodai said that he will not leave over anything, not a human descendant and not even a camel, that belonged to Amalek. Rabbi Eliezer says that Hashem said that one can accept a convert from any of the nations of the world except for Amalek. According to Rav Elazar Hamodai, Shaul’s war had the normal parameters of a war against Amalek.
Which opinion do we accept? The one major decisor on this issue is the Rambam. He does not mention any instructions to destroy the animals, and he implies that Amalekites who want to convert are exempted from the destruction bound for their nation. According to him, Shaul’s instructions went beyond the halachic norm, which can help us understand why he was so bothered by them. Even so, a prophetic command is fully binding, and Shaul was correctly criticized. As the gemara says, in the face of an explicit command, Shaul should not have allowed his humanism to make him "overly righteous."