According to the Talmud (Megilla 16b), the truth to which this verse refers is the requirement for a kosher Megillas Esther scroll to be written with etched lines in the parchment.
The Maharal explains the symbolism of etched lines. First, H-Shem is straight in the sense of the letter of the law, but He is nevertheless kind. A line is also with no set beginning or end, like Torah, like Purim, and like H-Shem Himself.
Rav Yitzchak Hutner writes that etched lines refer to our hearts (parchment) on which the truth of Torah should be inscribed.
In the Rashbam’s commentary on the Torah (Bireishis 24:65), he writes that a grammatical rule, the word hazeh (“this”) refers to a close object, whereas the word halazeh (“ this”) refers to an object that is far. Already in this word, Esther means that the person responsible is someone close-by.
Similarly, the Malbim distinguishes between the two words for enemy – tzar and oyev. According to him, based on a verse in the Torah (Bamidbar 10:9) a tzar is someone who has already done harm. Based on a different verse (Devarim 21:10), an oyev is someone who wants to do harm. Both definitions fit Haman. Accordingly, Esther is answering both of Achashverosh’s questions, the first of which was who did this. Her answer: the wicked Haman. In answering his second question of the motive, Esther responds that it is an adversary and an enemy.
Interestingly, she answers the second question first, and then the first question, as Rabbeinu Yonah in his commentary Mishnah (Avos 5:9) recommends for wise people to do when appropriate. Similarly, the Talmud often (see Brachos 2a) comments on the latter point of a Mishnah before commenting on the former.
R’ Dovid Feinstein and R’ Gallico write that Esther was saying that Haman is evil and dangerous for all – not just for the Jews. This is based on the Midrash (Shemos Rabba 38:4), which quotes a verse (Devarim 33:27) that says H-Shem will push away all of our enemies. Regarding Haman, he is an enemy below as well as above; he terrorized our forefathers and he wants to terrorize our children; he is an enemy to me, and he is an enemy to you.
Similarly, Midreshai Torah write that Haman hates Achashverosh as much as he hates the Jews.
According to R’ Chadida, Esther is saying that Haman hates Jews for historical reasons, and therefore involving Achashverosh and his kingdom unnecessarily into an ancient feud. (Today also, many international leaders and their nations stumble into the Middle East quagmire without a thorough knowledge of the historic animosities and loyalties that are endemic to that region.)
The Alshich writes that Esther is saying that Haman is hated below and an enemy above.
The Targum translates this verse as: Haman wanted to kill you last night. After failing, he suggested wearing your clothes, and even the royal crown. H-Shem made it work out that Mordechai, a Jew garnered these honors, and now Haman wants the person who saved and represents you dead. As Yossipon points out, it is Mordechai who is looking out for conspiracies and plots against you.
The Lekach Tov writes that Haman is called by three descriptors because he had three intentions quoted by the verse (Esther 3:13) to destroy, to kill, and to annihilate the Jews.
Asking why the verse uses the word hazeh (“this”), the Ben Ish Chai explains that since all people have good in them, only the evil part of Haman should be hated. He quotes the AriZal’s (Shaar HaKavanos) interpretation of the Talmudic (Megillah 7a) practice of ad d’lo yada as advising us to only bless Haman when we are drunk. This means that inside our klipa (“shell”) we all hold great potential. After all, from Haman emerged his grandson, R’ Shmuel ben Shailot. That is the good trapped within him. The Talmud (Gittin 57b) famously says Haman’s grandchildren learn Torah. Although it says in Tehillim (97:10) to hate evil people, it means that we should only hate the evil part within those people. To see how far this goes, the verse that tells us to kill out Amalek (Shemos 17:14) tells us to destroy the remembrance of Amalek, since there is some good hidden deep within them.
The Talmud (Megillah 16a), also seemingly bothered by the amount of descriptions Esther uses for Haman, writes that Esther was actually going to point to Achashverosh, but an angel pointed her finger toward Haman.
R’ Meir Shapiro explains that the word hu means something outward, whereas zeh means something hidden. Here, Haman is the obvious, explicit enemy. Like any deft politician, Achashverosh can claim deniability, and wash his hands of the entire plan. The Talmud is saying that Esther is hinting to Achashverosh that she considers him equally guilty of the planned annihilation of the Jews.
On the other hand, R’ Dovid Feinstein writes that Esther was literally going to point to Achashverosh because she was upset with Achashverosh for claiming ignorance.
The Vilna Gaon explains that, like a Freudian slip, Esther pointed at Achashverosh at this point because it is the nature of people to say X if they are thinking of X, even when they consciously want to say Y. Since the righteous are constantly thinking of H-Shem, so Esther is pointing to the King.
The Chazon Ish asks why, at this critically sensitive time for the Jews, would Esther endanger their lives? He explains that she had inculcated the characteristic of emes (“truth”) to such a degree that she found it impossible to lie, implying that Achashverosh was innocent. H-Shem had to send an angel to save the day.
Similarly, the Ohel Moshe quotes R’ Puvarsky (Mussar V’Daas) that Esther’s body could only tell the truth. We have the power to train your body to copy your soul, as it says in Tehillim (63:2), “my soul thirsts for You, my flesh longs for You.” We have the ability to train our flesh to want what the soul wants, as it says in the Mishnah (Avos 2:4). Similarly, Chovos HaLevavos writes that introspection will benefit you in both worlds, as it says in Tehillim (119:59) “I consider my ways, and I turn my feet to Your testimonies.” That is the foundation of mussar philosophy, that the goal of self-improvement.
The Maharal points out that Esther would be lying saying that this was entirely Haman’s doing, since Haman could do nothing without Achashverosh. The verse in Tehillim (101:7) says, “He who performs deceit shall not dwell in My house.” A lie cannot save the Jewish people since geulah (“redemption”) cannot result from falsehood.
R’ Hanoch Leibowitz answers the question somewhat differently. He explains that Esther, having been forcibly taken to be his wife for twelve long years, subconsciously hated Achashverosh. She therefore pointed at him, though he was not entirely responsible for decree. Even great ones err when affected by their subconscious desires. If such a one as Esther can fall prey to such desires, all people must plan out their actions before doing anything, and then think back and investigate the motivations and results of all behaviors.
R’ Eliyahu Lopian says that the angel saved Esther because no harm can come to one who is performing His Will, like speaking the truth.
The Torah in Bamidbar (33:55) commands the Jews entering the land of Canaan that they must drive out all bad influences from there, or else the remainders would be “thorns in your eyes, and pricks in your sides” which Ramban interprets as spiritual blindness and physical harassment. Perhaps this verse can also refer to Haman, who forced everyone to bow to his idol, and he tried to physically annihilate the Jews.
Also interestingly, the gematria of tzar (90+200=290) (“adversary”) is the same as the word pri (80+200+10=290) (“fruit”), whereas the gematria of oyev (1+6+10+2=19) (“enemy”) is the same as the name Chava (8+6+5=19). Perhaps this hints to the Talmudic dictum (Chullin 139b) that the verse about the tree in Gan Eden (Bireishis 3:11) alludes to Haman.
R’ Avigdor Miller points out that fasting for three days is difficult, and accomplished an unprecedented amount of teshuva.
The Talmud (Yevamos 121b) uses this verse to inform us that it is difficult, although not miraculous to be without food for that long.
The Midrash (Esther Rabbah 8:7) writes that these three days corresponded with the 13th, 14th, and 15th of Nisan, which included the first day of Pesach. When questioned regarding why Pesach should be foregone, Esther pointed out that there would be no Pesach if the Jews were wiped out.
The M’nos HaLevi quotes from the Yalkut Shimoni that these three days were the 14th, 15th, and 16th of Nisan. The Ohel Moshe points out that the main difference is whether or not the Jews of Persia had the second Seder.
The Maylitz Yosher writes that the Jews were expected to fast on Pesach in order to shock them into realizing the seriousness of their predicament.
The M’nos HaLevi writes that the three days correspond to three sins regarding which Esther expects to be guilty: eat non-kosher food, submit herself to Achashverosh, and partial complicity in the death of Hasach.
Rabbeinu Bachya writes that H-Shem only challenges tzaddikim for three days. For example, when Avraham went to potentially sacrifice his son, he found Mount Moriah in three days (Bireishis 22:4). Also, when the brothers were taken by Yosef, they were imprisoned for three days (Ibid. 42:18). Furthermore, Yonah remained inside the big fish that swallowed him for three days (Yonah 2:1). R’ Dovid Feinstein writes that the three sections of the Written Law (Torah, Nevi’im, and Kesuvim) were given to three groups of Jews (Kohanim, Levi’im, and Yisroelim) for which they needed to prepare for three days (Shemos 19:11).
The Ben Ish Chai writes that the Torah affects us on three different levels: thought, speech, and action. Therefore, Esther was telling Mordechai that the Jews need to prepare these three days to perform honest repentance through thought, speech, and action.
The Ginzei HaMelech quotes the Vilna Gaon (on Bireishis 27:13) that when Rivka told the nervous Yaakov to place the blame of his upcoming deception “eilai” (“on me”), this word can be an acronym for Eisav, Lavan, and Yosef. Those may be the greatest of Yaakov’s tests in life, that came along with the blessing he gets from his father.
Also, the Ginzei HaMelech points out that these are three different types of people: Eisav represents a glutton; Lavan represents idolatry, and Yosef represents the challenge of intermarriage. These same three issues are the ones for which Jewish existence was threatened in the Purim story. Pri Tzedek quotes from the Zohar on Chukas that the three patriarchs, Avraham, Yitzchak, and Yaakov, represent three characteristics: kindness, awe, and truth. These are the polar opposites of the three characteristics which, according to the Mishnah (Avos 4:21), destroy one’s life: jealousy, lust, and honor. During these three days, then, Esther wanted the Jews to perfect themselves in these three areas.
The Ben Ish Chai points out that three days is 72 hours, and this is the gematria of chesed, (“kindness”) (8+60+4=72). Therefore, the Jews were supposed to spend these days evoking H-Shem’s Kindness.
R’ Avraham Sutton points out that 72 is also the gematria of H-Shem’s four-letter Name when each letter is spelled out with all the yuds included ([10+6+4]+[5+10]+[6+10+6]+[5+10]=72).