There are several things about this passage that are important to understanding it.
Probaton, the word translated “sheep”, would be better translated as “flock”, for it refers to any small 4-legged animal, not just sheep.
Eriphos, the word translated “goats”, would be better translated as “kids, baby goats”, which is what Eriphos specifically means.
Ethnos, the word translated “nations”. It occurs 164 times in the NT and is translated in the KJV 93 times (57%) as “Gentiles”, 64 times (39%) as “nations”, 5 times (3%) as “heathen”, and only 2 times (1%, this one passage) as “people.” Most “assume” that Jesus is speaking about God judging individuals; this perspective is even “translated” into this passage by translating ethnos as “people”. And yet, Jesus very well could be talking about groups of people, whether that be nations, communities, or ethnic groups. Or Jesus could be talking about Gentiles as opposed to the Jews. Jesus does not specify whether He is speaking of Gentiles vs. Jews, Gentile nations vs. Israel, or individuals; and yet this one fact is extremely important in understanding Jesus’ intended meaning of this passage. Is Jesus speaking of judging “individuals” or “nations”? And is he speaking of God specifically judging Gentile nations?
Who are “the least of these my brothers”? Many assume that because Jesus speaks of the sick, hungry, stranger, prisoner, thirsty, or naked, Jesus is speaking literally of the poor and disenfranchised of society; and this is possibly what He meant by “the least of these my brothers”. However, earlier in Matthew 24 Jesus is warning of the coming destruction of Jerusalem, and throughout scripture the word “nations” (ethnos, Gentiles) is often set in contrast the “Jews”, God’s “chosen” nation. So Jesus could be foreseeing the destruction of Jerusalem and the Jews being scattered to the nations. And recalling God’s promise to Abraham to bless those who bless him and curse those who curse him, Jesus could be warning of how God blesses the nations that bless the Jews and punishes the nations that mistreat the Jews.
In Matthew 24:9 Jesus also specifically warns His **disciples **that they will be persecuted by all nations because of following Him. “IF” Jesus is referencing this distinction then He could be warning of God blessing or punishing nations or individuals based on how they treat Jesus’ followers, Christians, the least of these His brothers. This is certainly reflected in other passages of scripture meant to encourage persecuted believers.
Jesus could also be speaking of social justice, how individuals or nations treat the poor and disenfranchised of society among them. Scripture is certainly replete with admonitions to and promises for taking care of the poor, the sick, the strangers among us. And if this passage was in Luke then I would think this would be Jesus’ intended meaning because Luke has a theme of social justice. But this is Matthew who wrote primarily to the Jews. But then again, in this passage Jesus is speaking to His followers, the disciples, and might be literally warning of how we, his disciples treat the poor and disenfranchised, “the least of these”.
Kolasis, translated punishment, specifically means remedial punishment and would be better translated as chastizement.
So the shepherd separates the kids from the flock so that the kids can be chastized, trained. Why? So that they can function well as part of the flock. Goats are very independent and need training to be more communal. This fits with the “maturity” issue of people who are so self-centered that they don’t even see the needs of people around them, much less seek to meet those needs.
Frankly, the more I study this passage and the more I study Jesus’ teachings, the more I think that Jesus used this non-specific language to speak of diverse but similar messages, all of which are true! In other words, in this passage Jesus is warning of at least seven different but similar perspectives. He is warning Gentile individuals and/or nations to be careful of how they treat the Jews among them. Jesus is also warning people, individuals and/or groups concerning how they treat His disciples. And Jesus is warning everyone, individuals, nations, and especially Christians concerning social justice, how they treat the poor and disenfranchised of society! Seven similar but diverse messages, like facets of a diamond, they are diverse colors but from the same light! Different perspectives but all true!
Is it any wonder then that Jesus would use the non-specific wording of aionian life and aionian punishment to reference God intervening in a person’s, nation’s, or church’s life based on how they treat people, especially the Jews, Christians, or poor and disenfranchised. Included in this Jesus could even be warning majority Christian groups about how they treat minority Christian groups, the rich about how they treat the poor, the in crowd about how they treat the ones on the fringes. It is a powerful passage! And to interpret it to be about those who are saved vs. those who are not-saved is to nullify it of it’s power! Believers say to themselves “Hey, no worries for me, I’m saved.” And unbelievers say to themselves either “I don’t care what is says,” or “Look, I’m just as good as most believers I know, so I’m good to go to.” So it speaks to no one if interpreted to be about saved and unsaved.