Sefer Gedulas Mordechai quotes the Rov of Alik zy”a as saying in the name of “men of wisdom” that the true “g’mar chasimah tova” is on Chanukah. He says that only those who understand the secrets of Chanukah understand the connection between the chasimah and Chanukah and the connection between Chanukah and Yom Kippur.
He adds that Parshas Vayeishev is connected to Rosh Hashanah. This is the reason we read the Haftorah that contains the words: “Will a shofar be blown in the city and the nation will not tremble?” And Parshas Mikeitz is connected to Yom Kippur. Just like we confess our sins on Yom Kippur, on Parshas Mikeitz we read, “Es chata’ai ani masker hayom!” (I admit my sin today.)
Furthermore, we kindle lights on Chanukah, just like on Yom Kippur. The lights of Chanukah symbolize how every Jew can reach the level the Kohen Gadol reached when he kindled the menorah in the holy of holies. We also add a new light every night to represent the kohen’s counting of “achas v’achas...”
Sefer Tzemach Dovid sees the idea of a g’mar din being sealed on Chanukah from the verse (Tehillim 90:3): “Tasheiv enosh ad daka... You bring man to the crushing point, and You say, ‘Return, sons of men.’” This indicates that one can still do teshuva until “daka”, which has a gematriah of 25, i.e., the 25th day of Kislev.
