According to Malbim, since the previous verse (Esther 8:15) testifies to the fact that everybody was happy, the various expressions in this verse underscore the fact that the Jews were especially joyous.
Rav Samson Raphael Hirsch (Collected Writings, Volume III, 405) writes that this verse demonstrates that the Jews could now survive any difficulty in history because they “preserved their own light and joy.”
The Rambam (Perakim Hatzlacha, Chapter 2) emphasizes that all of the good that the Jews received was due to their return to Torah. Based on this, the Binyan Shlomo points out that it is a very praiseworthy custom to learn Torah on the holiday of Purim (see Rema, Orach Chaim 695:2).
The Sharis Yosef teaches that objects going from darkness to light is yet another source for the customto wear costumes on Purim.
The Talmud Yerushalmi (Brachos 1:1) writes that this description mirrors how the Jews will be redeemed with the coming of Moshiach.
The Talmud (Megillah 16b) interprets this verse’s expressions thus: light is Torah; happiness is Yom Tov; joy is circumcision; and glory is tefillin.
Rashi comments on the Talmud that Haman made decrees forbidding Jews from fulfilling these mitzvos. The Yad HaMelech points out that Jews may have neglected circumcision at that time, as they sometimes have done on times of persecution to pass as non-Jews.
The Megillas Sesarim writes that Mordechai’s wearing tefillin earlier (Esther 8:15) put that mitzva back in vogue.
Rav Shimon Schwab finds it impossible for the Jews to have been successfully banned from these mitzvos, en masse. Rather, he explains that the Jews at that time studied Torah, but without light; they commemorated holidays, but without happiness; they performed circumcisions, but without joy; they wore tefillin, but without glory. Without caring, without thinking, and without these precious mitzvos affecting their souls.
Rav Yehonason Eibshutz points out that it is a natural, human reaction for the emotional impact of an event to fade in subsequent anniversaries of that event. For instance, as happy as a child’s birthday celebration may be, it pales in comparison to the happiness felt at the actual successful birth. However, when that event is attached to a mitzva that is repeated every year, the original happiness felt at the event is retained (and perhaps enhanced) with the performance of the mitzva. This is the reason for the Talmud to equate happiness with Yom Tov; with each occurrence of Purim, its mitzvos reignite its accompanying joy.
The Sfas Emes asks a fundamental question: why does the verse uses metaphors instead of explicitly writing that the Jews garnered Torah, Yom Tov, circumcision, and tefillin? He answers that, with the miracle of Purim, the Jews recognized the real nature of light, happiness, joy, and glory; light comes from Torah, happiness comes from Yom Tov, joy comes from circumcision, and glory comes from tefillin.
The Ohr Gedalyahu adds that all of these misapplied emotions point to the Jews’ ancient battle against Amalek, a nation described (Devarim 25:17) as having cooled us. Amalek wins when Jews perform mitzvos without an accompanying fire of emotion. He quotes the Sefer Yetzira that the month of Adar is represented by the letter kuf, meaning kedusha (“holiness”), which he defines as keeping something special and invigorating.
The Ohel Moshe similarly writes that simcha (“happiness”) is the antidote to Amalek’s cooling effect. The Vilna Gaon notes that all four of these mitzvos – Torah, Yom Tov, circumcision, and tefillin – are regularly called osos (“signs”) and eidus (“testimonies”). He explains that these all testify that there is one G-d, and that the Jewish people are uniquely His people. He adds that taking the first letters (roshei teivos) of the words ora (“light”), simcha (“happiness”), sasson (“joy”), and yikar (“glory”) – aleph, sin, sin, and yud respectively – produces a gematria (1+300+300+10=611) equal to that of Torah (400+6+200+5=611). He continues by quoting a cryptic Talmudic tale (Sukkah 48b) about a character named Sasson speaking with another named Simcha. In this piece of Aggadeta, the two are trying to outdo each other by quoting verses throughout TaNaCh in which one or the other appears first. When Sasson and Simcha finally consult with Rebbe Abahu, he tells them that if a person has a water flask but never fills it, but merely keeps it next to him, he will die of thirst.
The Vilna Gaon’s explanation is beyond the author’s erudition and the scope of this work, but the Shem M’Shmuel explains that conversation by distinguishing between the exact spiritual nature of these two almost synonymous emotions, happiness and joy. He writes that happiness is the emotion felt after careful planning yields a successful result, whereas joy is the emotion felt when one experiences an unexpected windfall. The debate between Sasson and Simcha, then, is whether success is better felt in the former type of situation, or the latter. For instance, should an organization carefully plan its charitable giving, or bypass the planning and initiate the giving as quickly and haphazardly as possible? Having one necessarily means lacking the other. Rebbe Abahu’s allegoric answer, then, is that there needs to be spiritual content (water) inside the emotion (water flask) to gain anything beyond failure (thirst). Therefore, in our verse, the Jews had both emotions – happiness from the prearranged success, and joy from the unexpected success.
The Ginzei HaMelech wonders why the great mitzvah of teshuva (“repentance”) seems missing in this list of mitzvos the Jews are performing. After all, the Talmud (Megillah 14a) says that Achashverosh giving his signet ring to Haman created the greatest wave of teshuva in history. He answers that exactly these mitzvos are actual teshuva! Sitting around feeling sorry is not genuine repentance; improving our performance of H-Shem’s service is how we return to Him.