During Passover, we read the following passage, from Exodus 12:12:
וְעָבַרְתִּי בְאֶרֶץ מִצְרַיִם בַּלַּיְלָה הַזֶּה, וְהִכֵּיתִי כָל בְּכוֹר בְּאֶרֶץ מִצְרַיִם מֵאָדָם וְעַד בְּהֵמָה וּבְכָל אֱלֹהֵי מִצְרַיִם אֶעֱשֶׂה שְׁפָטִים, אֲנִי יי.
And God said, "I will go through the land of Egypt on that night… and I will mete out justice against all the gods of Egypt. I the Eternal.
God Himself is saying that He will fight other gods. How can God fight other gods, if other gods don't exist?
The "gods" worshipped by ancient Egypt included the Nile, cows and the sun (see e.g., Wikipedia's entry). These definitely exist as physical entities.
One of the goals or effect of the ten plagues was to show God's dominion over these entities. The Maharal (cited in R Shmuel Goldin's Unlocking the haggada, p. 115) explains one can break down the plagues in three groups
In total the plagues demonstrated God's total dominion over the entire world.
A very important theological question that confuses many.
In Biblical Hebrew, the word אלהים means "powers" in general, but can be used either as a Holy Name (referring to G-d) or to any other source of power be it human (like kings or judges) or inanimate, like celestial bodies, natural phenomena or imaginable figures (god of fire or god of fertility).
THe difference in reading verses with the name אלהים is that the first is forbidden to say in vain and the others are not (see Rambam Yesodey Hatorah 6) even if they are written the same.
So what G-d is saying in this passage, is that His intention is to show that all the powers of all other gods that people worship come from one G-d, and without Him they are powerless.
Rabbi Eliezer Ashkenazi as cited by Rabbi Yaakov Tzvi Meklenburg in HaKsav VeHaKabbalah writes that it refers to people who were born under the Mazalic influence of Ares whom the Egyptians venerated as quasi-gods and to firstborns whom the Egyptians also venerated.
