The Parable of the Sheep and the Goats
The King separates the nations by one measure: what they did for the least of these.
When the Son of man comes in glory, he separates all nations as a shepherd divides sheep from goats. The sheep fed the hungry, clothed the naked, and visited the prisoner — and are astonished to learn they did it to the King himself. The goats did none of it. Inasmuch as ye have done it unto one of the least of these, ye have done it unto me.
The parable
For I was an hungred, and ye gave me meat: I was thirsty, and ye gave me drink: I was a stranger, and ye took me in: Naked, and ye clothed me: I was sick, and ye visited me: I was in prison, and ye came unto me.
I was an hungred, and ye gave me meat... the sixfold mercy the King remembers.
And the King shall answer and say unto them, Verily I say unto you, Inasmuch as ye have done it unto one of the least of these my brethren, ye have done it unto me.
Inasmuch as ye have done it unto one of the least of these my brethren, ye have done it unto me.
What it means
This is less a parable than a preview of the last judgment, and its measure is startling. The King identifies himself completely with the hungry, the stranger, the sick, and the prisoner — so that ordinary acts of mercy toward the overlooked turn out to have been done to Christ himself.
Both groups are surprised. The righteous do not remember serving the King — their mercy was so natural it left no self-conscious record. The others do not remember failing him — their neglect was equally unconscious. The judgment reveals what was really going on beneath a lifetime of small choices about the needy.
The passage does not teach that good deeds earn salvation, but that genuine faith inevitably shows itself in compassion, especially toward the least of these. Where there is real love for Christ, there is real love for the people he loves; and where there is none, the claim to know him rings hollow.