1)
What freedom is Hashem calling?
1.
Rashi: You are free from Me. I am not your Master to save you. You are Hefker to the sword and hunger [Radak - and plague]!
2.
Malbim: One who is Eved Hashem, he is free from chance occurrences. Nothing else rules over him. When one goes free from Hashem's Reshus, he is 'under' (vulnerable to) chance occurrences, like I explained above (refer to 15:2:2:2). This was a punishment for seizing slaves and transgressing the Bris.
2)
Why is it written l'Zava'ah, and we pronounce it "l'Za'avah"?
1.
Radak: Both of them refer to motion, just the letters are reversed, like Kesev and Keves and other such words.
