Why Does the Pasuk Say There Was In the Past Tense

Why does the Megillah say: אורה היתהליהודים – “for the Jews there was light”, using the word היתה, which means “there was”, which is past tense?

The Nachal Eshkol explains: The sefer Medrash Eliyohu (R’ Eliyohu HaKohen of Izmir) learns that Haman was happy when the lots he cast fell on Adar because the plague of darkness in Mitzrayim took place in that month. His mistake, however, was failing to realize that the Torah states: “For all the Children of Yisroel there was light in their dwellings” (Shemos 10:23). The Megillah is thus telling us that the foundation upon which Haman built his hopes to annihilate the Jewish people was illusory because he miscalculated and failed to realize that there was light then for the Jews in Mitzrayim.