“not of this sheep pen” means not found within Judaism. Jesus did not come exclusively for the Jews; He came to save the whole world (John 3:16). This was not a new concept, but was instead foretold throughout the Old Testament (Isaiah 42:6, 49:6, 56:8). However it was a concept which the Jews were not eager to accept. They thought that the other nations of the world were to either become their slaves or be destroyed. Barclay observes that “One of the hardest things in the world to unlearn is exclusiveness.”

John 3:16  “For God so loved the world that he gave his one and only Son, that whoever believes in him shall not perish but have eternal life.

Isaiah 42:6  “I, the LORD, have called you in righteousness; I will take hold of your hand. I will keep you and will make you to be a covenant for the people and a light for the Gentiles,

Isaiah 49:6  he says: “It is too small a thing for you to be my servant to restore the tribes of Jacob and bring back those of Israel I have kept. I will also make you a light for the Gentiles, that you may bring my salvation to the ends of the earth.”

Isaiah 56:8  The Sovereign LORD declares—he who gathers the exiles of Israel: “I will gather still others to them besides those already gathered.”

“must” = indicates the necessity Jesus experienced when He thought of saving the Gentiles. It was not a whim of His, nor was it expedient; it was necessary.

“one fold” (KJV) is a mistranslation. Previous in this verse Jesus speaks of other sheep who are not of this fold. The word used there is “aule” which means “sheepfold” or a roofless area enclosed by a wall in open country in which shepherds keep their flocks for the night. But here the word is “poimne” which means “a flock of sheep.” This is not a fold, it is the flock. This mistranslation has been falsely used by some to teach that there can only be one church (theirs of course) and that outside of that church there is no salvation.

one flock = Jesus was saying that there would not be a Gentile church and a Jewish church; they were to be united in one flock. Although there may be many folds there is only one flock. Christians are to be in unity but this can only happen because we have one shepherd, Jesus.

Egerton Young was the first missionary to the indians in Saskatchewan. He found them and told them of the love of God, the Father. After he had given them his message, an old chief came up to him and said, “When you spoke of the great Spirit, just now, did I hear you say ‘Our Father’?” “Yes,” said Egerton Young. “That is very new and sweet to me,” said the chief. “We never thought of the great Spirit as Father. We heard Him in the thunder; we saw Him in the lightening, the tempest and the blizzard, and we were afraid.  So when  you tell us that the great Spirit is our Father, that is very beautiful to us.”  The old man paused, and then he went on, as a glimpse of glory suddenly shone on him.  “Missionary, did you say that the great Spirit is your Father?”  “Yes,” said the missionary.  “And,” said the chief, “did you say that He is the Indians Father?”  “I did,” said the missionary.  “Then,” said the old chief, like a man on whom a dawn of joy had burst, “you and I are brothers!” (qt’d by Barclay)  The only possible way that men can have unity is for them to be sons of God.