"I am the good shepherd, and know my sheep, and am known of mine.
15 As the Father knoweth me, even so know I the Father: and I lay down my life for the sheep.
16 And other sheep I have, which are not of this fold: them also I must bring, and they shall hear my voice; and there shall be one fold, and one shepherd."
It is unfortunate that sometimes it seems that much of today's Bible teaching is without much real investigation and thought. The above verse is often misused to assign a group of people, who never had any promises made to them, the recipient of becoming a part of the sheep fold. What should happen is for the person doing the study to ask the question what does the scripture say about "other sheep who are not of this fold".
The implication is that there are two sheep folds. Both have sheep in them. At the time Christ spoke what we find in John 10 there was only one fold hearing his words. When he then brought the other fold they would all hear his voice and become one fold. The two folds would become one fold as if they had been divided and now would become one.
Most of us have been taught that the other fold has to be the "Gentiles" or non-Israelites however in order to justify that one must find scripture that either later explains John 10 specifically or prophesied to John 10 as it's fulfillment. I do not find any scriptural justification for this answer to John 10.
There are several scriptures however that talk about a division that occurred and a prophesied reunion of Israel. After the death of Solomon his son Rehoboam refused to hear the people's request for lower taxes and from that point forward in the old testament there were two separate groups of Israelites. Rehoboam found himself ruling over two tribes, Judah and Benjamin, both together known as the house of Judah, improperly called "Jews" in the English translations. Jeroboam then became the ruler over the ten tribes to the north which became known as the house of Israel.
I am using the proper names for these groups. As mentioned the term Jew is a misnomer and should never have been in the scripture. Check the Hebrew and Greek and also the context to see what the word should have been. The first instance of it's use in the old testament finds the "Jews", properly known as the house of Judah fighting against Israel, in this case properly, the house of Israel. Abraham, Moses and King David were not Jews. Abraham was a Hebrew while Moses and King David were Israelites of the tribes of Levi and Judah respectively. If you had called someone of the tribe of Levi a Jew they would have corrected you.
Both houses of Israel were for the most part wicked from that point forward. The house of Israel was the worst and not much good is said about it compared to a few good kings for the house of Judah. The prophecy in the book of Hosea showed that God would send the ten northern tribes away into the Assyrian captivity. However it was never intended to be a permanent captivity just as the Babylonian captivity was not permanent. Hosea chapter one has Hosea prophesying that the northern ten tribes who are prophetically referred to as "not a people" would at one point in the future be called "sons of the living God" or as I tell people, Christians. You can find the phrase "not a people" and "not my people" in the new testament (KJV) and it refers to the northern tribes as in Romans 9:25-26. Note that Paul even tells us to go look in the book of Hosea.
"Yet the number of the children of Israel shall be as the sand of the sea, which cannot be measured nor numbered; and it shall come to pass, that in the place where it was said unto them, Ye 'are not my people', there it shall be said unto them, Ye are the sons of the living God.
11 Then shall the children of Judah and the children of Israel be gathered together, and appoint themselves one head, and they shall come up out of the land: for great shall be the day of Jezreel."
Notice that the prophecy has the two houses reunited under one head, that is Christ, and that they would leave the land. This is exactly what happened from the time when Christ was here. From that point forward many of those of both houses of Israel became known as Christians. When the ten tribes were sent away it was called a divorce by Jeremiah in chapter 3. They lost the right to be called Israel, which means "ruling with God". So the scripture correctly never calls them Israel from the time of their exile. You must look at the context, but most every time you see the term Gentile the context is actually referring to them. Gentile is a Latin word meaning "kin of the same race". The Greek word behind Gentile is "ethnos" where we get the English word ethnic. An example for the word Gentiles is in Romans 2:14-15. The text demands that the Gentiles referred to were descended from Jacob Israel based on who was given the promise of the law being written on the heart, Hebrews 8:8-10, Hebrews 10:16 and Jeremiah 31:31-33.
Besides the parable of the Prodigal son, this prophecy is also answered in the second chapter of Ephesians.
I will not quote the entire chapter, but as you read through it notice several key words and phrases that are important and find connection to the ten tribes. "Ye who sometimes were far off", "the middle wall of partition", Reconcile, (you can not reconcile two people who were never at one time one people), "Far off and near" (This phrase is used elsewhere for the two houses of Israel.), Christ made peace between the two houses and brought them together again. This was not a physical reunion until those in Judea began to spread out into which lands the northern tribes were already living. As you begin reading the chapter think of the ten northern tribes and not some non-Israelite people.
One final word for those who still think that the northern tribes did not exist in the time of Christ and the apostles. Here is first a quote from Josephus.
"...wherefore there are but two tribes in Asia and Europe subject to the Romans, while the Ten Tribes are beyond the Euphrates till now, and are an immense multitude, and not to be estimated by numbers." Flavius Josephus, historian and contemporary of the Apostle Peter.
"James, a servant of God and of the Lord Jesus Christ, to the twelve tribes which are scattered abroad, greeting."
It is sad that some now teach that the twelve tribes in James 1:1 really meant "the church". They only teach that because they do not see that James meant exactly what he said and we should take it exactly that same way. Why would he say "twelve tribes" if he meant something else? I like to take the approach that what the scripture says in the Hebrew and Greek is what the author meant and it is our job to figure it out, not decide that it really means something else.