What is the meaning of "va'Ta'at"?
Rashi: This is like va''Ta'af; it has the same root as Ayit 1 (Bereishis 15:11).
Radak: Refer to 14:32:1:2.
Michtav me'Eliyahu (5, p. 431): One should be concerned for everything, that it is a Kli for spirituality. Sometimes one is concerned for it amidst yearning for Gashmiyus, even if he does not use it. Sha'ul's revealed intent was for Korbanos; Shmuel countered that in the depth of his heart, he veered for spoils. It was difficult in his eyes to destroy a tool for Gashmiyus.
Mishnas R. Aharon 1 p.187: The people veered after spoils [and you did not oppose them]. Refer to 15:20:3:1.
What are the rebukes in this verse?
Malbim: There are three. (a) You did not heed Hashem's word. This is unlike a person who commands, for then it suffices to fulfill his intended purpose, even if he is not meticulous about the details and the means. When Hashem commands, every detail and means is an end unto itself - heeding Hashem's word precisely! Anything less is not a Mitzvah at all. You thought that it suffices to avenge and destroy Amalek - who can know Hashem's intent?! (b) You veered for spoils, amidst craving wealth. (c) You did evil in Hashem's eyes - one who detracts from a Mitzvah, he transgressed "v'Lo Sigra" (Devarim 13:1), and did not fulfill the Mitzvah.
