1)
Why does it say "Matzasi David Avdi"?
1.
Radak: I know that he is My servant, and I will not find another like him.
2.
Malbim: This corresponds to Emunah, based on the recipient's preparation. I found him prepared, for he is Avdi.
2)
What is "b'Shemen Kodshi"?
1.
Radak: It is Shemen ha'Mishchah, which is called "Shemen Mishchas Kodesh" (Shemos 30:25).
2.
Malbim: This corresponds to Chesed, without consideration of preparation. I put an influence of supreme Kedushah on him via anointing him. Before, it discussed his Gevurah and defeating his enemies; here it discusses his spiritual happiness and Kedushah.
