1)
Why does it say "ha'Omed Bein ha'Hadasim"?
1.
Malbim: The angel stood amidst the Tzadikim of the generation. This angel was appointed to oversee Yisrael; he guards the Hadasim, i.e. Tzadikim.
2)
Is the entire land serene?
1.
Radak: The Nochrim are serene, and Yisrael are in pain. This is why the angel said "Ad Masai Atah Lo Serachem Es Yerushalayim" (12).
2.
Malbim: Yes ? the wars ceased, for they already conquered the entire land. He also hinted that now they will not harm Yisrael. Yisrael initially dwelled in the shade of Malchus Yavan in serenity.
