1)
What is the significance of "Mi ve'Chatzer"?
1.
Malbim: This was Hashgachah - the Rasha came to hang the Tzadik, the moment after the king realized that Haman's grandeur really belongs to Mordechai!
2)
What do we learn from "He prepared [a gallows-pole] for him"?
1.
Megilah 16a: He prepared it for himself. Vilna Gaon - there was a decree [to eradicate the Jews - refer to 4:1:1:1]. One might have thought that also this (hanging) was initially decreed on Mordechai, and later switched to Haman, The Gemara teaches unlike this. From the beginning, it was decreed on Haman alone, and not on Mordechai.
