1)
Why does it say "Al Yedei Moneh"?
1.
Radak #1: Yisrael are compared to Tzon. The shepherd is the king. The shepherd normally counts his flock to see if one is missing.
2.
Radak #2: This refers to eradicating sinners from Yisrael when they leave exile, like it says in Yechezkel - "v'Ha'avarti Eschem Tachas ha'Shavet" (Yechezkel 20:37).
3.
Malbim: After discussing a place of flock, the entire nation is compared to flock. The shepherd counts to see if any are missing.
