In speaking of the final judgment, Jesus says, “All the nations (τὰ ἔθνη) will be gathered before him, and he will separate the people (αὐτοὺς) one from another (ἀπ᾿ ἀλλήλων) as a shepherd separates the sheep from the goats.”
Someone asked a while back why the pronoun is masculine (αὐτοὺς) and the antecedent is neuter (ἔθνη)?
The primary answer is that Jesus is about to speak of separating people, sheep and goats, not separating nations, so he has to draw attention to the fate of individual people. The shift to the plural masculine pronoun does this (see Dad’s commentary on Matthew, p. 236).
While ἔθνη is grammatically neuter, it is certainly not conceptually neuter since “nations” are comprised of “people.” While strict grammar rules would require a neuter pronoun, I can see how an author would switch to a masculine (i.e., generic) pronoun when thinking of the people that make up the nations. This is why the Holy Spirit can be referred to with a masculine pronoun even though πνεῦμα is grammatically neuter (Jn 15:26; but not always, see Jn 7:39; 14:17).
I was checking Craig Blomberg’s commentary on this verse and he pointed out something I had not realized. “Palestinian shepherds frequently had to separate their flocks this way. Sheep and goats freely intermingled and often looked quite similar in appearance, at least from a distance. We too could probably not guess from superficial knowledge and external appearance who are truly God’s people, but he knows” (396). At a distance, you also could not see the wolves in sheep’s clothing (Matt 7:15).