Back to the sheep and goats. I see the terms are used interchangeably with wheat and tares and has a 1st century application.
Matt 25 "sheep and goats" is a continuation of Matt 24. Jesus is speaking to his disciples rather than sending a general broadcast message for all future generations:
Mat 10:16 Behold, I send you forth as sheep in the midst of wolves: be ye therefore wise as serpents, and harmless as doves.
Mat 10:22 And ye shall be hated of all men for my name's sake: but he that endureth to the end shall be saved.
Mat 10:23 But when they persecute you in this city, flee ye into another: for verily I say unto you, Ye shall not have gone over the cities of Israel, till the Son of man be come.
The above is spoken to HIS contemporary disciples.
So lets look at the context of the goats and sheep:
Mat 25:33 And he shall set the sheep on his right hand, but the goats on the left.
Mat 25:34 Then shall the King say unto them on his right hand, Come, ye blessed of my Father, inherit the kingdom prepared for you from the foundation of the world:
Notice next:
Mat 25:40 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.
Jesus is speaking of his contemporary brethren that were to proclaim the gospel, the goats would be those Jews/Israelites in the cities of Israel and the nations where the gospel was being spread, the goats rejecting and persecuting them in the councils and synagoguess during the 40 years after Christ death.
Mat 10:17 But beware of men: for they will deliver you up to the councils, and they will scourge you in their synagogues;