Many of the commentaries that I have place Matthew 25:31 and following at the end of time, or the end of the Gospel age. Some don’t even have Christians participating in this judgment, because they had been removed from the earth in the previous age. Yet, nothing like this appears in the plain reading of the scripture. Nothing is said about the end of time. That has to be brought to the table by the person interpreting the scripture. In other words, it is a doctrine of men, because it cannot be found in the scriptures. Neither could the end of the Gospel age be a proper interpretation, because no such thing is ever mentioned in scripture (cf. Daniel 2:44). It, too, is a doctrine of men. What does the scripture actually say?
Jesus told his Apostles that he would come with his angels and sit on the throne of his glory. At that time all nations would be brought before him, and he would separate them as a shepherd divides the sheep from the goats—the sheep to the right and the goats to the left. To those on the right Jesus says, “come you blessed of my Father, inherit the kingdom prepared for you from the foundation of the world” (Matthew 25:31-34; emphasis mine).
That’s quite a statement that God had the Kingdom prepared “from the foundation of the world.” Those at Jesus’ right were to inherit that Kingdom, and according to most commentary scholars, immediately upon the realization of God’s plan, all things come to an end—sort’a, kind’a like “…and they lived happily ever after!” End of story. Well, I don’t think the scriptures do that kind of thing.
Notice what Paul says in his letter to the Ephesians:
Ephesians 1:4-10 According as he hath chosen us in him before the foundation of the world, that we should be holy and without blame before him in love: (5) Having predestinated us unto the adoption of children by Jesus Christ to himself, according to the good pleasure of his will, (6) To the praise of the glory of his grace, wherein he hath made us accepted in the beloved. (7) In whom we have redemption through his blood, the forgiveness of sins, according to the riches of his grace; (8) Wherein he hath abounded toward us in all wisdom and prudence; (9) Having made known unto us the mystery of his will, according to his good pleasure which he hath purposed in himself: (10) That in the dispensation of the fullness of times he might gather together in one all things in Christ, both which are in heaven, and which are on earth; even in him. (emphasis mine)
God’s plan of salvation incorporated Paul’s readers even before the foundation of the world (verse-4), and he made known unto them the mystery of his will (verse-9). Why did he make this known to them? So that, “in the dispensation of the fullness of time he might gather together in one all things in Christ.” In other words, he made known the mystery of his will in order that the Gospel might be preached to the world in an effort to “gather together in one all things in Christ.”
Instead of time coming to an end at Matthew 25:31 and following, things were just getting started. Instead of the Gospel age coming to an end, we have Matthew 25:31 establishing the Gospel age, which, by the way never ends. We have inherited a Kingdom that cannot be moved (Hebrews 12:28). It doesn’t end here; it begins here. The Apostles asked about the end of the age (Matthew 24:3), well that is where we begin. The Gospel age was initiated at Pentecost, but it was established in 70 AD at the end of the age—the end of the Old Covenant.
Paul tells us that God’s plan to gather all things in Christ began to occur in “the dispensation of the fullness of times” (Ephesians 1:10, see above). Earlier Paul told the Galatians that “in the fullness of time” God sent his Son, born of a woman, made under the Law (Galatians 4:4). Moreover, it is claimed by the writer of Hebrews that Jesus had come and spoke to us in the last days (Hebrews 1:2). So, the last days, i.e. when Jesus initiated the Gospel, were also called the fullness of time.
Therefore, those who inherit the Kingdom (Matthew 25:34), inherit a Kingdom that cannot be moved (Hebrews 12:28). That is, it cannot be destroyed, nor does it end (cf. Daniel 2:44). Moreover, this same Kingdom had been prepared for the heirs from the foundation of the world, and the heirs had been incorporated into God’s plan from before the foundation of the world, and that in order to bring salvation to the world by preaching the Gospel (Ephesians 1:10). In other words, Matthew 25:31 and following is the beginning of the Gospel age.
 The statement “from the foundation of the world” refers to the time of Adam’s rebellion. The phrase in the Greek is repeated elsewhere in the New Testament eleven times, always translated “foundation of the world” except at Hebrews 11:11. I have a study about this called The Overthrow of the World, if anyone cares to read it.