Then the righteous ones will answer him with the words, ‘Lord, when did we see you hungry and feed you, or thirsty, and give you something to drink?

The “sheep” ask, “When did we see you?” indicating that Christ is invisible during his presence, judging them, not by what they do for him personally, for certainly as heavenly King he has no need for their earthly help. But they can see Christ’s “brothers,” and these brothers of Christ yet on earth often come into need.