From: http://www.catholic-forum.com/members/popestleo/onehope.html
"Jesus Has 'Other Sheep,' Earthly Sheep!"
John 10:16: "And I have other sheep, which are not of this fold; those also I must bring, and they will listen to my voice, and they will become one flock, one shepherd."
Traditional Christian belief has been that these other sheep are the Gentiles (starting in the first century) who would join Jewish believers and form one body of believers. Some say that Jesus was prophesying an earthly class to be formed nearly two thousand years later. Let's read something in the next chapter:
John 11:49-52: "But a certain one of them, Caiaphas, who was high priest that year, said to them: 'You do not know anything at all, and you do not reason out that it is to your behalf for one man to die in behalf of the people and not for the whole nation to be destroyed.' This, though, he did not say of his own originality; but because he was high priest that year, he prophesied that Jesus was destined to die for the nation, and not for the nation only, but in order that the children of God who are scattered about he might gather together in one."
In the very next chapter John speaks of the Jewish nation and others 'not of that nation,' who would be gathered into one. Wouldn't it be more likely that these Gentiles would be the other sheep? (Compare Ephesians 2:11-22.)