It's in the Bible: "Know ye therefore that they which are of faith, the same are the children of Abraham." Galatians 3:7. "For they are not all Israel which are of Israel; neither because they are the seed of Abraham are they all children… but the children of promise are counted for the seed." Romans 9:6-8.
The children of promise are those who put their faith in Jesus. It's in the Bible: "And if you are Christ's, then you are Abraham's seed and heirs according to the promise" Galatians 3:29.
Whether they are Jewish or Gentile, God regards only those who have renewed hearts as true Israelites. It's in the Bible. "For he is not a Jew which is one outwardly, nor is that circumcision which is outward in the flesh; but he is a Jew which is one inwardly, and circumcision is that of the heart, in the Spirit, and not in the letter' whose praise is not from men but from God." Romans 2:28,29, NKJV. "For we are the circumcision, who worship God in the Spirit, rejoice in Christ Jesus, and have no confidence in the flesh." Philippians 3:3, NKJV
God has a special covenant with those who are true, spiritual Israelites. It's in the Bible: "For this is the covenant that I will make with the house of Israel… says the Lord, 'I will put My laws in their mind and write them on their hearts; and I will be their God, and they shall be My people. None of them shall teach his neighbor and none his brother saying, "Know the Lord," for all shall know Me, from the least of them to the greatest of them. For I will be merciful to their unrighteousness, and their sins and their lawless deeds, I will remember no more." Hebrews 8:10-12. Compare with Jeremiah 31:31-34 and Ezekiel 36:26-28.
The Bible tells us the spiritual. characteristics of God's spiritual Israel. They are a morally clean people. It's in the Bible: "Truly God is good to Israel, to such as a pure in heart." Psalm 73:1. They are a people who are spiritually intimate with God. It's in the Bible. "He has exalted the horn of His people, the praise of all saints, even of the children of Israel, a people near to Him." Psalm 148:14.
They are a completely honest people. It's in the Bible. "I will mention the lovingkindness of the Lord … toward the house of Israel, which He has bestowed on them according to His mercies, and according to the multitude of His lovingkindnesses. For He has said, Surely they are My people, children that will not lie: so He was their Saviour." Isaiah 63:7,8. Speaking of Nathaniel, Jesus declared, "Behold an Israelite indeed, in whom is no guile!" Jn. 1:47. Also see Zephaniah 3:13.
God's True Israelites are keenly conscious of the saving merits of Christ's blood. It's in the Bible: "Wherefore remember, that ye being in time past Gentiles in the flesh, who are called Uncircumcision by that which is called the Circumcision in the flesh made by hands; that at that time ye were without Christ, being aliens from the commonwealth of Israel, and strangers from the covenants of promise, having no hope, and without God in the world; but now in Christ Jesus, ye who were sometimes [once] far off are made nigh by the blood of Christ… Now therefore ye are no more strangers and foreigners, but fellowcitizens with the saints, and of the household of God." Ephesians 2:11-13,19, see verses 11-22, also Revelation 7:1-14.
The true Israel of God have been regenerated by the power of Christ's cross; they are held in the grip of its love and grace. It's in the Bible: "God forbid that I should glory save in the cross of our Lord Jesus Christ, by whom the world is crucified unto me, and unto the world. For in Christ Jesus neither circumcision availeth anything, nor uncircumcision, but a new creature. And as many as walk according to this rule, peace be on them, and mercy, and upon the Israel of God." Galatians 6:14-16.
Spiritual Israelites have their citizenship registered is the New Jerusalem in heaven. It's in the Bible: "For here we have no continuing city, but seek one to come." "A city which hath foundations whose builder and make is God" Hebrews 13:14; 11:10. "But ye are come unto mount Sion, and unto the city of the living God, the heavenly Jerusalem, and to an innumerable company of angels." Hebrews 12:22. This is the Jerusalem "above, which is free, the mother of us all" (i.e., all who have faith in Christ as their Redeemer. Galatians 4:26.
When God creates a new heaven and a new earth, His spiritual Israelites will then inhabit the New Jerusalem. God will set this city on earth and make it the spiritual capital of the Universe. It will be a city of peace that shall never be touched by apostasy, conflict, violence, or ungodliness of any kind. It's in the Bible: "And I saw a new heaven and a new earth: for the first heaven and the first earth were passed away… And I John saw the holy city, New Jerusalem, coming down from God out of heaven, prepared as bride adorned for her husband. And I heard a great voice out of heaven saying, Behold, the tabernacle of God is with men, and He will dwell with them, and they shall be His people, and God Himself shall be with them, and be their God. And God shall wipe away all tears from their eyes; and there shall be no more death, neither sorrow, nor crying, neither shall there be any more pain: for the former things are passed away… . And there shall in no wise enter into anything that defileth, neither whatsoever worketh abomination, or maketh a lie: but they which are written in the Lamb's book of life." Revelation 21:1-4,27.
Though respectful of human laws, spiritual Israelites do not regard any earthly government as God's supreme representative. Their spiritual citizenship and paramount affections are in heaven. "For our citizenship is in heaven, from which we also eagerly wait for the Saviour, the Lord Jesus Christ." Philippians 3:21. For, "You are a chosen generation, a royal priesthood, holy nation, His own special people, that you may proclaim the praises of Him who has called you out of darkness into His marvelous light" 1 Pet. 2:9.
But God's spiritual Israel does not to despise earthly government. It's in the Bible: "Let every soul be subject to the governing authorities." Rom. 13:1. Yet when there is conflict between human law and divine law, it is written, "We ought to obey God rather than men." Acts 5:29.
Love to God, faith in Christ as a personal Saviour, and reception of a new heart that gives cheerful and willing obedience to His laws is the essence of being a True Israelite. The names of all such are written the Lamb's book of Life. We have seen it in the Bible.