1)
What is the meaning of "Sakosah l'Roshi b'Yom Nashek"?
1.
Radak: On the day that they come to me with weapons - spear, arrows and all war weapons - You cover my head. I.e. You are a helmet of salvation for my head. Sakosah is past tense used in place of future; this is common [in Nevu'ah].
