Rashi explains that the verse teaches what those who lived through these times did, what motivated their actions, and what the consequences were of those actions.
As the Talmud (Megilla 19a) relates, Achashverosh used the Temple vessels because he thought the Jewish exile was permanent. As a result, he killed Vashti.
Mordechai was motivated to not bow down to Haman by Haman’s making himself an obecjt of worship, an avoda zara. As a result, the Jews merited a miraculous rescue.
Haman was motivated to eradicate the Jews by his anger over Mordechai not bowing to him. This resulted in his downfall and hanging.
Achashverosh was motivated to review his royal history by his fear of Esther and Haman plotting against him. This resulted in the honoring of Mordechai, the hanging of Haman, and the rescue of the Jewish people.
R’ Dovid Feinstein writes that the verse stresses “all the words” of this document because Mordechai wrote out all the words and details in Megillas Esther for future generations to know that they should do just as we are doing now – looking deeply into the words and letters of this holy work to glean from it lessons for our lives.
The Talmud (Yerushalmi Megilla 2:4) adds that this is the reason why Halacha (Shulchan Aruch, Orach Chaim 692:2, Mishna Berura 692:9) requires every Jew to hear every word of the public reading of Megillas Esther on Purim uninterrupted in order to fulfill their obligations.