God steps directly into the flock to restore order and establish justice. By emphasizing His personal involvement, God makes it clear that He is the ultimate ruler over everyone and will personally take charge of executing justice [מצודת דוד].
This judgment takes place within the flock itself, specifically between two very different types of animals. On one side are the fat, healthy, and strong sheep [מלבי״ם, רד״ק, ביאור שטיינזלץ, מצודת ציון, רש״י]. On the other side are the lean, frail, and weak sheep [רש״י, מצודת ציון]. God promises to intervene to protect the vulnerable. He will judge the strong, well-fed animals that use their power to harm the weak and frail ones [מצודת דוד].
Ultimately, this pastoral scene serves as a metaphor for human society. It represents God's judgment between the wealthy and the poor [רד״ק].