Why are we specifically told that Mordechai was an Ish Yehudi as it says in the pasuk (Ester 2:5):
אִישׁ יְהוּדִי, הָיָה בְּשׁוּשַׁן הַבִּירָה; וּשְׁמוֹ מָרְדֳּכַי
Would we assume he wasn't a Jew if we weren't told this? If we would know he was a Jew without the Pasuk specifically mentioning it, what is the reason for mentioning it?
As always, please cite your sources.