The Bible makes it clear that God chose Israel — not just Judah — to be His nation (Deut. 7:6). He made a covenant with them when He brought them out of bondage in Egypt. See chapters 9 through 24 of Exodus. Israel was to be an example to all nations of the blessings brought by obedience to the laws of God. They were His chosen people — not His favorite. God has no favorites (Acts 10:34).
Yet, Israel failed. They rebelled constantly and sinned. They split into two nations — the house of Israel and the house of Judah. God sent Israel into Assyrian captivity about 720 B.C. They became lost in history. He later sent Judah into Babylonian captivity, starting about 604 B.C. Their territory was occupied and the people transplanted en masse to Babylon in 587 B.C.
Seventy years later Judah began to return, and the rebuilding of Jerusalem and the temple was begun. However, the Jews again misapplied God’s commandments. They added many of their own laws under the influence of the Pharisees (Matt. 15:1-9; Mark 7:1-13).
Jesus said the Kingdom would be taken from them and given to others — to spiritual Israel, that is, to the Church (Matt. 21:43). The Church now comprises God’s chosen people (I Pet. 2:9). All who are converted are reckoned to be children of Abraham (Gal. 3:29). The Church is to marry Christ as His chosen bride at His return from heaven in this generation (Rev. 19:7-9).
Nonetheless, God has not given up on national Israel! Prophecies in Hosea 2, Ezekiel 36, and Zechariah 12-14 show that the people of Judah and Israel will repent and reunite and again become God’s people. They will be the leading nation in the world tomorrow (Zech. 8). Of course, the Church will then be immortal and under Christ will rule the physical nations (Rev. 2:26; 3:21; 5:10; 20:4-6).
In summary, Israel, that is, the house of Israel and the house of Judah united, will again be God’s chosen nation. In the world tomorrow they will fulfill the job God called them to do 3500 years ago.