The apostle Paul knew nothing of lost tribes. Standing trial before Festus and Agrippa, Paul explained: “the hope of the promise made of God unto our fathers: Unto which promise our twelve tribes, earnestly serving God day and night, hope to attain” (Acts 26:6-7). All twelve tribes in Paul’s day had the same hope.
James knew nothing of lost tribes. He wrote his letter to “the twelve tribes which are scattered abroad (or, of the Dispersion)” (James 1:1). Though they were taken from Palestine at different times, James writes to all twelve tribes. They were not lost.
There is Anna of Asher (Luke 2:36), Paul of Benjamin (Phil. 3:5), and many Levites in the NT. No others are identified in the NT as out of Judah. But who in the NT was identified as in the tribe of Judah? Jesus and his family. That is all. Aside from Jesus’ linage (and Levites), tribe membership was no longer an important issue.
Only one text in the NT makes a distinction between Israel (ten tribes) and Judah (two tribes). Heb. 8:8 quotes Jer. 31: “Behold, the days come, says the Lord, when I will make a new covenant with the house of Israel and with the house of Judah.” One “new covenant” includes both houses. It’s the covenant Jesus spoke of when he took “the cup after supper, saying, This cup is the new testament in my blood, which is shed for you” (Luke 22:20). (“Covenant” and “testament” is the same Greek word here.) Since Hebrews declares the fulfillment of Israel and Judah having a new covenant, we are forced to believe it happened. The ten tribes of Israel were not lost; they took part in the new covenant.
Generally, “Israel” and “Jews,” (from Judah), are interchangeable terms in the NT. At Pentecost, “there were dwelling at Jerusalem Jews, devout men, out of every nation” (Acts 2:5). In verse 22, Peter addresses these Jews as “men of Israel.” Israelites are Jews; Jews are Israelites. Where did these Jews come from? Many places. Here’s one example. 2 Kings 18:11 had said that “the king of Assyria did carry away [the ten tribes of] Israel unto Assyria, and put them in… the cities of the Medes,” (among other places). Who was present on Pentecost? Among others, Luke lists “Medes” (Acts 2:9). Surely, some, if not all, of these Median Jews would have been from the ten tribes of Israel.
In the OT we read of three (or four) “returns” from captivity. We often think that was it. But Acts 2 tells us differently. Jews were present “out of every nation under heaven.” Before the captivity God-fearing Israelites from the north had joined themselves to Judah and Jerusalem. Centuries later in Acts 2, we see Jews/Israelites from Media and all over the world returning to Jerusalem to worship. Surely, A.D. 30 was not the first time Jews from all over the world came to Jerusalem to worship. They had no inkling that anything out of the ordinary would happen that day.
Neither did all these Jews just come as pilgrims. Jerusalem had many foreign-born Jews with established residence. Read Acts 6:9 to see that the Jews who stirred up trouble for Stephen belonged to a synagogue of immigrant Jews. It is not difficult to deduce that throughout the centuries between “the return” from captivity and the beginning of the church, Jews of all tribes kept returning to Jerusalem either to live or in pilgrimage to the feasts.
In the first century, Paul and James recognized the existence of all twelve tribes. God-fearing members of the ten tribes were surely among converts to Christ, whether in or out of Jerusalem. In order to fulfill Jeremiah’s prediction of the new covenant with Israel and Judah, members of the ten tribes of Israel had to be among the converts. Tribal identities may well have been often lost as these Israelites assimilated into one nation of Jews, and then further assimilated into the church of the new covenant. Lost by assimilation. Ezekiel had predicted: “join them one to another into one stick” (37:16-20). In the New Covenant, there is no distinction between Israel and Judah. More than that, “there is neither Jew nor Greek… for you are all one in Christ” (Gal. 3:28).