כִּ֤י אֲנִ֣י יָ֭דַעְתִּי כִּי־גָד֣וֹל יְהוָ֑ה וַ֝אֲדֹנֵ֗ינוּ מִכָּל־אֱלֹהִֽים׃
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Siftei Chakhamim
He did not leave any idol. . . Otherwise, how would he know [that Hashem is greater than all the gods]? You might object: Referring to Dovid Hamelech it is written, “For I know that Hashem, our Master, is greater than all gods” (Tehillim 135:5). Re”m answers: Dovid knew it through practical exploration rather than logical explanation. Whereas Yisro said, “Now I know.” I.e., he knew this because of all the deeds that Hashem [just now] did. It was not through the wonders [that He performed]. If so, how did Yisro know this? Perforce, by [comparing Hashem’s deeds to that which he knew from previous] exploration. Another answer: Here it is written, “Yisro said, ‘I know that Hashem is greater than all the gods.’” Due to the definite article, it means: “. . .Greater than all the gods, who are known to me and to no one else.” How did Yisro know this to be true? Perhaps someone else also explored, as he did, and also has this knowledge. Perforce, [Yisro knew this to be true] because “Yisro did not leave any idol unworshipped.” [But Dovid said, “Greater than all gods,” without the definite article.]