What is "Meshicho"?
Rashi: It is grandeur, like "Lecha Nesatim l'Mashchah" (Bamidbar 18:8).
Rashi (citing Megilah 12a): It is Melech ha'Mashi'ach. Hashem complains about Koresh to Mashi'ach. (I said that he should build My house and gather My exiles, but he said 'who will go up among you
How did He hold his right hand?
Malbim: I brought him to the war, conquest and authority.
What is "l'Rad Lefanav Goyim"?
Rashi: He spreads and flattens Goyim in front of him.
Radak: Larad is Makor (like an infinitive). It is like "ha'Roded Ami Tachtai" (Tehilim 144:2), spreading and flattening. The Targum of "va'Yrak'u Es Pachei ha'Zahav" (Shemos 39:2) is u'Rdidu.
Malbim: He will be Rodeh (rule over) them harshly
What is the meaning of "u'Masnei Melachim Afate'ach"?
Rashi: It is an expression of weakness and breaking strength. Girding the loins is invigorating strength - "Ezar Na ch'Gever Chalatzecha" (Iyov 38:3), "v'Atah Tezar Masnecha" (Yirmeyah 1:17). (Hashem will untie their belt!)
Malbim: He will not fear other kings, for I will untie the sword from the belt on their loins.
What will Hashem open in front of him?
Rashi: The doors of the gates of Bavel. Sha'arim are the interior of the opening of the gate; the doors are what open and close the gate.
Radak: It will be as if they are open. Similarly, it will be as if they do not close, for it says "Dalsos Nechushah Ashaber" (2).
Malbim: Even the inner doors, which are normally closed, I will open in front of him. All fortified cities will be open in front of him.
