The underlying meaning of v’nahafoch hu is that what initially is perceived as a cause is really an effect, and what seems to be an effect is really the cause.
Haman was hanged on the 17th day of Nissan (see Rashi on Megillas Esther 4:17). Yet, Mordechai waited until the 23rd of Sivan to send the new royal missives throughout the kingdom (8:9). Why? Why not send the new letters immediately? The Gra explains that one of the reasons for this delay was so that Klal Yisrael would daven for a total of seventy days, corresponding to the seventy years of galus Bavel, the end of which they were at (pirush red, Megillas Esther 8:9).
This comment of the Gra, if you really think about it, is astounding in its implications!
Essentially, Haman’s demise meant the nullification of the death threat on Klal Yisrael. Nevertheless, Mordechai wanted them to think that they were still in mortal danger so that they would daven from the depths of their hearts, pouring out their souls to the Ribono shel Olam. Seventy days of this highest level of tefillah was necessary.
There were two facets to this necessity of seventy days of tefillah. The Gra says that each day of tefillah corresponded to one of the years of galus Bavel. During those years, there was no avodah in the Beis HaMikdash. Tefillah is called avodah she’balev, and it functions as a stand-in for avodas ha’korbanos. The seventy days of tefillah was necessary to make up for the lack of avodah in the Beis HaMikdash for seventy years. Yom la’shana. Furthermore, the implication of the Gra’s words is that they needed the zechus of this tefillah in order to leave galus Bavel, return to Eretz Yisrael, and rebuild the Beis HaMikdash.
It stands to reason, then, that it was for the sake of these seventy days of tefillah that the whole gezeirah of Haman had to happen. V’nahafoch hu! What at first appears to be a circumstantial, ancillary effect of the events that took place – namely, the teshuva and tefillah of Klal Yisrael in their time of tzarah – was actually the whole cause and reason for all of the events of Purim to begin with!
Another result of the events of Purim was the hadar kibluha b’ahava (Shabbos 88a). Because Klal Yisrael was so inspired by the miracle that Hashem did for them, they reaccepted the Torah with love (Rashi ibid). Once again, this would seem to be an incidental effect of the events that took place. In truth, though, this was a root cause of all the events of Purim.
There is a famous statement of the Pirkei Heichalos that during the time period of the second Beis HaMikdash, HaKadosh Baruch Hu opened up the gates of wisdom. The primary manner in which this was manifest was throught the development of Torah shebaal peh. It was specifically during the period of Bayis Sheini that the full depth and power of Torah shebaal peh emerged and came to the fore.
However, there was a serious problem. At Matan Torah, HaKadosh Baruch Hu suspended Har Sinai over Klal Yisrael like a barrel and told them, “If you accept the Torah, great; and if not, your burial place will be right where you are.” Therefore, there was a potential for a moda’ah rabah l’Oraysah – that Klal Yisrael could claim their acceptance is not truly binding since there was a significant element of coercion involved (Shabbos 88a).
But what, you may ask, with naaseh v’nishma – that Klal Yisrael willingly initiated full acceptance of the Torah? The Medrash Tanchuma on parshas Noach says that Klal Yisrael’s declaration of naaseh v’nishma was in reference to Torah shebichtav, and the kafah aleihim har k’gigis was for Torah shebaal peh. Torah shebaal peh is the part of Torah that demands one to put forth great exertion and toil. When one begins a sugya, he is in the dark. It is the part of Torah that requires the most of a person. That is why they needed to be coerced, to a certain degree, to accept it.
Now, at the close of galus Bavel, the tekufah of Bayis Sheini is about to commence. The time period which will mark the seminal development of the chachmah of Torah shebaal peh. But that cannot happen so long as the modaah rabah l’Oraysah is still around. Chochma cannot be given to those who are not truly prepared to work on it. It was absolutely necessary, therefore, that this modaah rabah be nullified. This, then, is one of the major reasons that Purim had to happen. V’nahafoch hu! The hadar kibluha b’ahava is not an incidental effect of the Purim experience, it is a root cause.
Chazal tell us that HaKadosh Baruch Hu first puts the mechanism for salvation in place, and only subsequently brings about the tzarah. Thus, Esther was firmly ensconced in the royal palace before Haman’s horrible decree was issued (Megilla 13b).
But let’s think about this for a moment. What caused Haman’s terrible ire to be roused to the point that he wanted to do away with all of the Jews? Of course, it was the fact that Mordechai refused to bow to him. Take note, though, of the following words of the pasuk: “And all the servants of the king that were stationed at the gate of the king would kneel and bow to Haman…and Mordechai would not kneel and he would not bow (3:2).” It is clear from the pasuk that this requirement for everyone to bow to Haman was only for those stationed b’shaar hamelech, by the king’s palace, and not in all 127 countries under the dominion of Achashverosh. As such, had Mordechai not been at the shaar hamelech, the events of Purim would never have taken place! And what brought Mordechai to find himself daily at the gate of the king’s palace? Esther! Because Esther was in the palace, Mordechai frequented there to keep as much of an eye on her as possible. It emerges, then, that v’nahafoch hu: the refuah of Esther being in the palace was itself what caused the makah!