1)
Why does it say "Havu la'Shem Kevod Shmo"?
1.
Rashi (from Rosh Hashanah 32b): This is the source to say Kedushas ha'Shem (ha'Kel ha'Kadosh). There are 18 names of Hashem in this Mizmor; corresponding to them, they enacted 18 Brachos in Shemoneh Esre.
2.
Malbim: In addition to being Sheluchim to destroy, show honor to Hashem via bowing, i.e. abating when you come to the place of His Shechinah.
2)
What is the meaning of "Hadras"?
1.
Radak: It is honor, like "v'Hadarta Pnei Zaken" (Vayikra 19:32).
