Amillennialists, Postmillennialists, and even some Premillennialists view the Sheep/Goat judgment of Matthew 25:31-46 and the Great White Throne judgment of Revelation 20:11-15 as being the same event. But a close examination reveals that these two judgments are not the same judgment.
1. The timing of the Sheep/Goat judgment happens in connection with the second coming of Christ (see Matt 25:31-32). Jesus comes in glory with His angels, sits on His glorious throne and all the nations are gathered before Him. The Great White Throne judgment takes place after the return of Christ (Rev 19) and the thousand year reign of Christ with the saints (Rev 20:4-7). After the thousand years are completed (20:7) the Great White Throne judgment takes place (20:11-15).
2. The purpose of the Sheep/Goat judgment is to see who will inherit the kingdom (Matt 25:34) and who will not (Matt 25:41). The purpose of the Great White Throne judgment is to see who will be sent to the lake of fire (Rev 20:15)
3. The subjects of the Sheep/Goat judgment are both believers and non-believers—sheep and goats (Matt 25:32). The subjects of the Great White Throne appear to be unbelievers. While Rev 20:11-15 does not exclude the presence of believers at this judgment believers are not mentioned as being at this judgment. But unbelievers who are sentenced to the lake of fire at the Great White Throne judgment are mentioned (Rev. 20:15).
4. The basis of judgment at the Sheep/Goat judgment is how the nations treated the “brothers” of Christ (Matt 25:40). The basis of the Great White Throne judgment is works (Rev 20:13).
5. The subjects of the Sheep/Goat judgment appear to be those alive at the time of the second coming of Jesus. There is no mention of a resurrection of the saved and unsaved dead. The Great White Throne judgment says it is the dead who are raised for this judgment (Rev 20:13). The sea and Hades give up their dead for this judgment.
6. The Sheep/Goat judgment does not mention a “Great White Throne” being present while the Great White Throne judgment does (Rev 20:11).
7. The Sheep/Goat judgment does not mention the “book of life” being present while the Great White Throne judgment does (Rev 20:12).
8. The Sheep/Goat judgment does not indicate that death and Hades are thrown into the lake of fire while the Great White Throne judgment does (20:14).
9. The fact that there are two resurrections separated by a thousand years (see Rev 20:4b-5) strongly suggests that there can be two judgments separated by a thousand years.
(NOTE: Some also argue that the setting of the two judgments is distinct with the Sheep/Goat judgment being on earth while the Great White Throne judgment is in space since heaven and earth have fled away. While this argument is possible my view is that the Great White Throne judgment is also on earth since Rev 20:13 makes reference to the “sea” which still exists. In my estimation, heaven and earth flee away in the sense that they provide no hiding place for the wicked from God.)