Matthew 25 : 31 - 46 describes the Judgement of the Nations, which most commentators or theologians believe to be a description of the final judgement of mankind at the end of time to decide who will be saved or enter the kingdom.
I suspect this is not a correct interpretation for the following reasons .....
1. This is a judgement with consequences in the ages to come. If it happens at the end of time, there are no ages left for the consequences to be played out.
2. It is a judgement of nations or tribes, not individuals. The salvation of individuals is not involved, and, in any case, the salvation of individuals is not a matter of works or the offering of charity, but is a gift to all.
3. This story is the last piece of Jesus' answer to His disciples' questions that were asked at the beginning of chapter 24 involving the destruction of the temple, which occurred in AD 70 and before the generation to whom Jesus was speaking passed away (Matt 23 : 36 and 24 : 34).
4. It is a parallel with Matthew 16 : 27 - 28 (compare with Matt 25 : 31 - 33) in which Jesus assured his listeners that at least some of whom would personally see.
5. The nations referred to were probably the tribes of Israel, or the tribes of the land. Matt 24 : 30 calls them so, and back then historians like Josephus regularly referred to the nation of the Galileans, the nation of the Samaritans, etc. within the land of Israel.
Jesus told his disciples to "go and teach all nations" and I think He was understood to be referring to the ethnic groups within Israel or Judea because of their surprise when they eventually discovered Gentiles being saved in the mid and later chapters of Acts. (Acts 10 : 14 and 11 : 18.
It's also worth noting that Jesus told his disciples that they wouldn't have finished going through the cities of Israel before Jesus was to return (Matt10 : 23), thus expecting them to be spreading the gospel to Israel or Judea, and that Paul stated that the Gentiles being included in the gospel was a mystery prior to his revelation (Eph 3 : 6).
I therefore, as an uneducated bush theologian, prefer to view this judgement as one on the tribes or nations of Israel in AD70, and Jews being law-keepers, would be judged on how well they kept the law and offered charity to those who lived in the land with them.
That's where I'm up to, but I'm always learning.
Comments, as always, would be most welcome.