My New King James includes the word “mystery” six times in six chapters in the Book of Ephesians, written by Paul. This was a new revelation in the early church.
THE MYSTERY OF CHRIST
The Mystery of Christ is that we, true believers in Messiah, are ONE body.
how that by revelation He made known to me the mystery …. 4 … the mystery of Christ, 5 which in other ages was not made known to the sons of men, as it has now been revealed by the Spirit to His holy apostles and prophets: 6 that the Gentiles should be fellow heirs, of the same body, and partakers of His promise in Christ through the gospel,
This is an incredible mystery: that the Gentiles should be fellow heirs! “Gentile” is translated from the Greek “éthnos” meaning having a similar culture. And truly all cultures will be before the throne of God:
After these things I looked, and behold, a great multitude which no one could number, of all nations [G1484], tribes, peoples, and tongues, standing before the throne and before the Lamb, clothed with white robes, with palm branches in their hands,
The Israelites were given the Torah, the prophets, and “the adoption, the glory, the covenants, the giving of the law, the service of God, and the promises.” (Romans 9:4)
But if you have believing faith in Jesus the Messiah, you are a “new creation” in Christ! We have the promise of His Holy Spirit and thereby we are one body!
WORD OF CAUTION
There are deceivers that are sent into churches to lead the sheep astray! We are NOT ONE body with the deceivers! But the LORD said, in the parable of the tares (weeds), “Let both grow together until the harvest” so you don’t do harm to the real wheat or true believers. (Matthew 13:24-30)
See also FOR & AGAINST UNITY
STUDY GUIDES from HELPS Word-studies (Biblehub)
1484 éthnos (from ethō, “forming a custom, culture”) – properly, people joined by practicing similar customs or common culture; nation(s), usually referring to unbelieving Gentiles (non-Jews).