1)
Why does it say "v'Hishkarti... v'Yashnu Shenas Olam"?
1.
Refer to 51:39:2:1-2.
2.
Targum Yonasan: So they will die a second death, and not come to the world to come ("v'Lo Yakitzu").
2)
Why does it say "Ne'um ha'Melech Hashem"?
1.
Radak: He is King over every king, and He can remove kingship from whomever He wants and give it to whomever He wants.
3)
Why does it say "Hashem Tzevakos Shemo"?
1.
Radak: He is the Master of legions above and below. So is His name, and so is He!