The word “mystery” in the Greek refers to something that is hidden. It doesn’t mean it can never be known; it means it can only be known as God reveals it. Hebrews 1:1 explains that “God, who at various times and in various ways spoke in time past to the fathers by the prophets, has in these last days spoken to us by His Son, whom He has appointed heir of all things, through whom also He made the worlds.”
God moves according to His preset chronos times. Galatians 4:4-5 is one example. “But when the fullness of the time had come, God sent forth His Son, born of a woman, born under the law, to redeem those who were under the law, that we might receive the adoption as sons.”
In Romans 11, the Apostle Paul explains that Israel was cut off for a time because of their rejection of Jesus as the Christ or Messiah. Yet he also said that at the appointed time they would be grafted back in, “for the gifts and the calling of God are irrevocable” (vs. 9). In other words, God is not done with Israel. Hosea 6:1-2 prophesied that the Jews would be torn and stricken (cut off) for two great Days, the 2,000 years of the Church Age. On the third Day, they will be revived.
This is the same Third Day that Jesus referred to in Luke 13:32 as our Day of Perfection at the rapture. When we are gathered to our Lord Jesus Christ, the Jews will be accepted into the family of God as part of the redeemed when they finally recognize Jesus as the Messiah.
God’s appointed times and callings do not change. The Scriptures do not support a so-called “replacement theology.” Israel is God’s portion of the nations that He declared for Himself. It is His land. No other nation has usurped this particular calling. Of course as the Creator, He is the God of all the nations, whether or not they acknowledge Him (Psalm 2).
Galatians 1:3-4 tells us the next stage of the mystery of Christ: “Grace to you and peace from God the Father and our Lord Jesus Christ, who gave Himself for our sins, that He might deliver us from this present evil age, according to the will of our God and Father.” That deliverance comes at the dawn of the Appointed Day (Acts 17:31), the Day of the Lord, the 7th Day of God’s great prophetic Week.
We escape to stand and execute God’s judgment against the rebellious nations as joint-heirs with Christ. Our ruling judgments also bring deliverance to the Jews, for they will then be our brothers and sisters in Christ.
Hebrews 3:1 calls this our heavenly calling. It doesn’t say our earthly calling because we will reign with Christ over the earth from Heaven above during this 7th Day that lasts for a 1,000 years.