The Gemara asks: why don’t we say Hallel on Purim? Rav Nachmon explains the reading of the Megillah itself is the Hallel. HaRav Hutner zatzal adds this means by reading the Megillah we are fulfilling the saying of Hallel. This idea is mentioned in slichos on Taanis Esther as it saysלקרות כבהלל מהודים , to read the Megillah as with Hallel, praising and thanking Hashem. I heard from Avi Mori, the Meiri says according to this reason if a person does not have a kosher Megillah to use and he won’t be fulfilling the reading the Megillah, he will need to say Hallel.
The Gemara brings, Rava explains that since we were still servants of Achashveirosh after the Purim miracle, there is no requirement to say Hallel. The Meiri says according to this reason if one won’t have a kosher Megillah there is no requirement to say Hallel.
The Sha’arei Teshuva says it is possible that according to everyone there’s no requirement of Hallel since the Rabanan never instituted for Hallel itself to be said. He concludes that in the situation that one doesn’t have any Megillah he should say Hallel without a bracha.
HaRav Hutner says that most Rishonim disagree with the Meiri and hold even if one does not have a Megillah there is no need to say Hallel. Why is this? He explains that Hallel is said in honor of a miracle, and the Hallel corresponds to the type of miracle which the people in that time experienced. The three Yomim Tovim of Pesach, Shavuos and Succos are celebrated because of leaving Mitzraim. At that time, Hashem performed clear and open miracles, such as the ten makkos and the splitting of the sea. Therefore, on these Yomim Tovim we say Hallel with the words of Hallel. The miracles of Purim however were hidden in seemingly natural sequence of events. Therefore, its Hallel is to be said in a hidden way. The reading of Megillah is not simply in the place of Hallel, but rather a special and unique type of Hallel; a hidden one!
May Hashem help us recognize and be aware of His continued hashgacha.