Revelation refers to the sealing of 12,000 from each of the 12 Tribes of Israel, with Dan (traditionally the tribe of the Anti-Christ) being replaced by Levi.
The Orthodox Study Bible notes (on Rev. 7:4-8): “The servants of God are sealed by the Holy Spirit. Extensive debates have taken place regarding the 144,000. Some regard the number as symbolizing the entire faithful Church as the new Israel (12 tribes times the churches of the 12 apostles times 1000–a number which means ‘a great amount’). Thus, the contention is that the number simply stands for completeness and perfection– twelve times twelve equals the perfect square. Slightly differently, some see the 144,000 as the Church militant, the Church on earth, and the white-robed multitude (vv. 9.10) as the Church triumphant. On vv. 9-14, the OSB commentary notes that the multitude from all nations worships before the throne of God, and “represents either the entire faithful Church–which lives in th spirit of its baptism ‘washed … in the blood of the Lamb’–or the righteous from all nations who were not members of the 12 x 12 x 1000,’ old covenant Isarel and the Church,” presumably meaning those who have converted to the Church.
As Hieromonk Seraphim Rose of blessed memory noted, following St. John Damascene, “at the end of time the Jews will be restored to Christianity, to Christ,” and as the Apostle indicated, as the falling away of the Jews meant “riches” for the Gentiles who had the opportunity to come into the Church, the restoration of Israel will be like a rising from the dead for the Jewish people, with Enoch and Elias turning their hearts to Jesus Christ (address to students at UCSC, 1981).
Archbishop Averky writes in his Orthodox Christian commentary on Revelation that the limited number may indicate how few of the people of Israel will be saved in Christ by comparison with the multitudes among the Gentiles. He quotes St. Andrew of Caesarea’s early commentary that the precise number from each tribe indicates the “fruitfulness of the apostles’ seeds,” in how the Jewish Apostles as Christians evangelized the world.
In addition, a mystical symbolism could be indicated by the unknown histories of the “ten lost tribes” in relation to their possible entwining with the peoples of other nations in the world at large over time.
Twelve symbolically, as the number of the Apostles and of the Tribes of Israel, includes 4 x 3, 4 being associated in premodern tradition with the Creation or cosmos (as in the four ends of the earth, the four winds, the four seasons, the Four Evangelists, and the four cardinal virtues*), and 3 with the divine, identified with the Holy Trinity.
In any case, the Orthodox Church is Israel fully realized as the Body of Christ.
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*Four “cardinal virtues” (meaning literally “hinge” virtues), a phrase first known to have been written in Latin by St. Ambrose of Milan, and also used by pre-Schism Latin Fathers Sts. Augustine, Jerome, and Gregory the Dialogist. They are usually identified as prudence or wisdom, justice, fortitude or courage, and temperance. This list of moral virtues is found in the biblical books the Wisdom of Solomon and in 4 Maccabees, and also in Classical Greek pagan philosophical writings. They are distinguished from the three theological virtues–faith, hope, and charity (love).