The Vilna Gaon points out that Mordechai provided these animals to the couriers because he wanted them to hurry. This, despite the fact that they were exhausted from having just traversed the largest nation in the world to deliver Haman’s original decree. Seeing that they were tired, he gave them the fastest possible horses.
The Malbim writes that Mordechai sent the messengers on horses in contrast with Haman. In explanation, R’ Chaim Kanievsky writes that Haman had plenty of time – he had eleven months. Mordechai is in a hurry to save lives.
Interestingly, the Talmud (Megillah 18a) writes that the sages were unsure as to the translation of the couriers’ transportation.
Rashi translates achashtirans as swift camels.
The Ibn Ezra writes that these are a species of mule. After all, the verse says they are bred from ramachs, and the Mishnah (Kilayim 8:5) considers a ramach a mare, mother of a mule. Also, the Arabic word, ramach means mare.
R’ Yosef Kimchi concurs and he adds that achash in Median means large and tiran (misrain) means two. Therefore, the combination of the two words means the mating of two large animals: the horse and the donkey.
R’ Samson Raphael Hirsch (Collected Writings, Volume IV, 286) translates rachash as a draft horse. Parenthetically, he adds that the symbolic meaning of these in TaNaCh indicates a reluctance to listening to one’s master.
R’ Yehoshua Leib Diskin writes that these untranslatable words answer another question from the Talmud (Megillah 3b), which says one must interrupt Torah learning to hear the public reading of Megillas Esther on Purim. This is also brought down as the Halacha (Shulchan Aruch Orach Chaim 687:2). The Halacha (Mishnah Berurah Orach Chaim 690:26) further states from this verse that one fulfills one’s obligation in Hebrew despite not knowing the meaning. But is not Megillas Esther also Torah?! Rav Diskin explains that it is not considered Torah study if one does not understand it. Understanding is an essential component of Torah study. Hearing the reading is still an obligation because persumei nisa (publicizing a miracle) is even greater than Torah study.
In answering this question, R’ Dovid Feinstein reminds us that the Talmud (Menachos 29b) says that H-Shem made Olam HaBa (the World to Come) using a yud. Therefore, Mordechai was saying that, in threatening the extermination of the Jews, the people who believed in the World to Come, Haman was actually attempting to subvert the authority of Heaven.
The Maharal writes that, by writing the word “baYihudim” with an extra letter “yud,” Mordechai was indicating the kind of Jews affected by Haman’s decree. The first yud represents the Jews in general, and the second yud represents those Jews willing to sacrifice their lives to sanctify G-d if the need arises.
The Tzemach Tzedek takes this idea one step further. In the beginning of Creation, H-Shem created within mankind two yetzarim (inclinations) (see Rashi to Bireishis 2:7). Haman, after all, did not discriminate – he wanted to kill all Jews, good or bad. Interestingly, later when the Jews are saved, the verse (Esther 9:15) spells out Yehudim with two yuds again to testify concerning them that the spirit of teshuva that enveloped the Jews at that time made it so the yetzer for evil had no affect on them.
Perhaps these last two verses are so long because, as the Kol Sasson points out, this verse contains every single letter of the Hebrew alphabet – even the five final letters. According to the AriZal, rare verses like this point to the greatness of Torah, which is written with the letters of the Aleph-Beis.
Perhaps the previous verse is even longer to emphasize that a verse’s significance does not come from its size, but from containing the holy letters of the Aleph-Beis.
Megillas Sesarim writes that the word “pur,” coming from the foreign language of the Persian nation that had dominion over the Jews, has a negative connotation. Had the verse used the word “goral,” it would have had a positive connotation – especially with its allusions to the Yom Kippur service. Since the lot decided when the ideal time to massacre the Jews, the verse uses the Persian word.
On the other hand, since the lots also helped precipitate Haman’s downfall, the verse uses the Hebrew word, as well. In a deeper answer, the Pachad Yitzchak writes that the Jewish people always had two kinds of adversaries in their history – the four nations in which they were exiled, and the seven Canaanite nations they had to eject upon entry to the Holy Land. Therefore, he writes, “pur” is translated to emphasize the dual nature of Haman, in that he was both (as an Amalekite) from the seven nations in Israel and (as a Persian officer) from the four nations of exile.