The Talmud (Megillah 15b) writes that the verse uses the passive form of the verb (“were read”) because the pages of the book read themselves, since the king’s servant did not want to.
The Maharal explains that the Midrash (Yalkut Shimoni 545, and see Ezra 4:8 with Rashi there) writes that the palace scribe was one of Haman’s sons. Therefore, explains the Maharal, since he changed all references to Mordechai to say Haman, this was only true in the public book. In the private book, the king would notice the obvious inconsistencies, and would therefore have more reason to suspect Haman of conspiring against him.
Targum Sheini writes that the scribe did not erase Mordechai’s name, but merely skipped over his name. Therefore, the angel Gavriel turned the pages to the missing text, and the pages read themselves.
R’ Yehonason Eibshutz asks why such a miracle was necessary. He answers that the Talmud (Shabbos 88a) writes that the Jews accepted the Torah at Har Sinai with the words “naaseh v’nishmah” (“we will do and we will listen”). After this, H-Shem lifted a mountain over them, and threatened to drop it over them if they would not accept the Torah. What was the reason for this if they had just done exactly that? Tosfos answers that the Jews accepted the Written Torah with complete enthusiasm, but not the Oral Torah. They re-accepted the Torah in the conclusion of Megillas Esther, when the verse (Esther 9:27) writes “kimu v’kiblu” (“they took and they accepted”). It became clear to the Jews that their downfall was caused in the beginning of the Purim story, where they ignored the words of the great leader, Mordechai. For this reason, these words which were not written down were given orally, mida kineged mida. Perhaps it is for this reason that this miracle happened on the second night of the Pesach holiday, since its observance is totally rabbinic.
As a proof of this phenomenon, the Rokeach points out that the words “hayamim viyihyu nikarim” (“days [Chronicles]. And they were read”) (5+10+40+10+40+6+10+5+10+6+50+100+200+1+10+40=543) have the same gematria as lomed kee hayu nikrayim me’atzmam (“we learn that they read themselves”) (30+40+4+20+10+5+10+6+50+100+200+1+10+40+40+70+90+40+40=806).
R’ Yitzchak Hutner writes that we can learn a fundamental philosophical rule from this verse. Namely, in life, we do not really accomplish anything; H-Shem just makes it look to us as if we do things. As a proof, he quotes the phrase (Vayikra 11:38) “kee yiton” (“if he placed”), which the Talmud (Bava Metzia 22b) says could be pronounced “kee yutan” (“if it was placed”) in the passive voice because despite a person’s intent to do something, the final act is completed only through H-Shem. We are all vessels, and H-Shem is the real Doer in this world.