The ninth plague was absolute darkness that descended upon Egypt for six uninterrupted days. Like the other plagues, this darkness demonstrated to the Egyptians G-d’s power over them. Additionally, the darkness enabled the Jews (who were not affected by it) to circulate among the Egyptians in order to see where they were hiding their wealth. Also, there were Jews who did not want to leave Egypt, and they died during the plague of darkness.
The Future Redemption
וַיֹּאמֶר ה' אֶל מֹשֶׁה נְטֵה יָדְךָ עַל הַשָּׁמַיִם וִיהִי חֹשֶׁךְ עַל אֶרֶץ מִצְרָיִם וגו':
(שמות י:כא)
G-d said to Moses, “Raise your arm toward the sky so that there will be darkness upon Egypt.”
Exodus 10:21
G‑d did not force those Jews who did not want to leave Egypt
to do so. By choosing to remain in Egypt, their lives lost all meaning and had
spiritually ended. In contrast, in the future Redemption, even those Jews who
do not consciously want to be redeemed will be taken out of exile. This is
because when G‑d gave us the Torah, He connected our essence with His essence,
making it impossible for us to really oppose our connection with Him.
Of course, we can go through the motions of opposing our
connection to G‑d, but this is only superficial. Sooner or later, our deep,
inner essence will surface, and this will make us all indeed worthy of being
redeemed.1
