Ezra 2 emphasizes the fact that the people who came back to the land of Judah from exile are to be considered as all Israel. This is clear from the facts that twelve leaders bring them up from Babylon (Ezra 2:2), the list consists of the men of the people of Israel (Ezra 2:2), and the final verse also refers to all Israel (Ezra 2:70).
In Ezra 1:5, the people who went back to Jerusalem are described as those coming from Judah and Benjamin. These are the tribes that made up the southern kingdom of Judah. In Ezra 2:2, they are referred to as Israel. There is thus no longer a distinction between the southern kingdom and the northern kingdom. With the return from Babylon, the complete people of God, everyone whom God loves and who belong to him, come back from exile.
The Bible does not tell us what to make of the people who did not return from exile. We are not told if they should be considered in the same light as Gentiles and if they sinned by not going back to Jerusalem.1 Some of the Jews who stayed behind in exile were very godly and devoted to God. Mordecai is one example of someone who did not go back to Jerusalem but was nonetheless still devoted to God (see the book of Esther). God certainly made use of the people that stayed in exile. At the time of the New Testament, the various synagogues that Jews had established throughout the Greek and Roman world were used by the apostle Paul as a platform from which the good news about Jesus Christ was shared.
One of the key truths we must learn from the lists in Ezra 2 is that God works to rescue all of his people. No one whom he wants to rescue from Babylon is allowed to stay behind.
The Lord does not work in history to save everyone. There are Gentiles and others whom he does not bring back to Jerusalem. There are also people who do not hear about Jesus Christ or who reject the gospel when they hear the gospel being proclaimed. God chooses in Christ to save a definite number of particular people out of the entire human race. He works in history to save a people of his choosing.
In Ezra 1:5 God worked to stir up the heart of his people. In Ezra 2 we find out who are the people that God has chosen to rescue from Babylon. In Ezra 2 we find out who are the people that God has chosen to give new life (Ezekiel 37:1–28).
If God works to save all his people, we must not think that it is our job to make people Christians. If you are a preacher, your task is to faithfully share the good news about Jesus Christ. It is not your job to change the message of the gospel in order to make it easier for people to believe. God will use the proclamation of the gospel to save his people. You must make sure that you are clearly explaining the gospel to as many people as possible and you must trust that God will use your proclamation to achieve his purposes.
1 Now these were the people of the province who came up out of the captivity of those exiles whom Nebuchadnezzar the king of Babylon had carried captive to Babylonia. They returned to Jerusalem and Judah, each to his own town.