Why Conceal Esther's Nationality?

Introduction

Why Keep Secrets?

Twice in the second chapter of the Megillah, we read that Esther concealed her identity.  When describing the maidens' preparations to approach Achashverosh, we are told:

After Esther is chosen as queen, once again the text records:

These verses suggest that, both before and after becoming queen, Esther kept her Judaism a secret.  In fact, it seems that she first revealed her nationality only many years later, at the second party when pleading for her life and that of her nation, "תִּנָּתֶן לִי נַפְשִׁי בִּשְׁאֵלָתִי וְעַמִּי בְּבַקָּשָׁתִי".

Why, though, was Mordechai so adamant that Esther hide her roots; what purpose did such secrecy play?  Mordechai's own Judaism was apparently known, and the text suggests that he himself freely shared this fact ("כִּי הִגִּיד לָהֶם אֲשֶׁר הוּא יְהוּדִי"). If so, what about Esther or her position made him suggest that she act differently?

Misguided Advice?

The question is strengthened in light of the subsequent events of the Megillah, where it turns out that Esther's concealed identity plays a large role in the potential annihilation of the nation.  After all, had Haman known Esther's nationality, it is very unlikely that he would have dared write an edict to destroy her people!

Other Questions

Several other questions are relevant as well:

• "אֶת עַמָּהּ וְאֶת מוֹלַדְתָּהּ" – The verse speaks of Esther's concealing both her "nation" and "birthplace".  Is there a distinction between the two?
• Repetition – Why does the text find it necessary to share the fact of Esther's secret twice?  Were there distinct reasons to hide her nationality both before and after becoming queen?
• Religious observance – What does the concealing of Esther's religion teach about her personal religious observance?   Does concealment imply non-observance?