The Church was a mystery that was not revealed in the Old Testament. The mystery was not made known until the appointed time and it was the Apostle Paul who was the human vessel chosen to receive this lofty new revelation. In Ephesians 3:3 Paul tells the reader that the mystery was made known to (him) by revelation. The Greek word translated as revelation is ἀποκάλυψις (apokalypsis), meaning disclosure, appearing, or manifestation.(1) This word probably sounds familiar. Revelation 1:1 reads The revelation of Jesus Christ, literally the apokalypsis of Jesus Christ. This is where we get the title of the Book.
Certain spiritual knowledge only comes by revelation. If God didn’t reveal it, we wouldn’t know it. The Bible clearly teaches this.
The natural person does not accept the things of the Spirit of God, for they are folly to him, and he is not able to understand them because they are spiritually discerned. - 1 Corinthians 2:14
The Apostle Paul was aware of this, and it’s why he prays the following at the beginning of his Epistle to the Ephesians:
I do not cease to give thanks for you, remembering you in my prayers, that the God of our Lord Jesus Christ, the Father of glory, may give you the Spirit of wisdom and of revelation in the knowledge of him, having the eyes of your hearts enlightened… - Ephesians 1:16-18
Through revelation a mystery was unveiled to Paul. The Greek word translated as mystery is μυστήριον (mystērion), meaning a hidden thing or a secret.(2) In the Greek speaking Ancient world this word carried with it the connotation of a religious secret that was only known to the initiated. Some Bible Scholars have translated mysterion as a sacred secret.(3) Ancient mystery religions in Bible times were secret cults that offered initiatory rites and secret knowledge only to their members. Readers in Paul's Day knew this. The application then is that God only reveals certain spiritual knowledge to those who are born again, those who are initiated into the Kingdom of Heaven as it were.
Like I said earlier, certain things we could not know unless they were revealed to us spiritually. Jesus the Eternal Son reveals or makes known the Father:
No one has ever seen God. The one and only Son, who is himself God and is at the Father’s side— he has revealed him. - John 1:18 (CSB)
And:
…no one knows the Son except the Father, and no one knows the Father except the Son and anyone to whom the Son chooses to reveal him. - Matthew 11:27
Knowing the Father requires revelation, it does not happen by default. In a similar way Paul received revelation - a mystery or a sacred secret - that had to be given. Without that mystery being given, Paul would not have known it. And what exactly is this mystery? We are told:
This mystery is that the Gentiles are fellow heirs, members of the same body, and partakers of the promise in Christ Jesus through the gospel. - Ephesians 3:6
People will say that the mystery is that the Gentiles are included in the covenant blessings of God, but this reading of the text is at best incomplete. Provision was made for Gentiles in the Old Testament. Jews knew that Israel was to be a light to the Gentile Nations.
Under the Abrahamic Covenant we are told that all families of the earth will be blessed (Genesis 12:3, see Galatians 3:8). Later Rahab (the Harlot from Jericho) and her father's household dwelled in Israel (Joshua 6:25). Rahab is included in the Genealogy of Jesus Christ (see Matthew 1:5). Ruth, a gentile Moabite, was determined to sojourn with her mother-in-law Naomi, declaring:
For where you go I will go, and where you lodge I will lodge. Your people shall be my people, and your God my God. Where you die I will die, and there will I be buried. - Ruth 1:16-17
Under the Law of Moses, resident aliens (gentiles or sojourners) were to be treated equally both in terms of the Law and social status (Leviticus 19:33-34, 24:22; Numbers 15:14-16; Deuteronomy 10:19). Gentiles were able to participate in worship with Israel. For example, alien families were able to observe the Passover if all the males were circumcised (Exodus 12:48). Gentile sojourners could also participate in the Feast of Pentecost (Deuteronomy 16:11), the Feast Tabernacles (Deuteronomy 16:14), and they were able to give acceptable offerings (Leviticus 22:17). They could also eat and be filled from the tithe of the produce during the harvest season in Israel (Deuteronomy 14:28-29).
Gentile inclusion in the Covenant Blessing of Yahweh is explicitly prophesied in Old Testament Scripture. Here are a few examples:
Now therefore, O kings, be wise;
be warned, O rulers of the earth.
Serve the LORD with fear,
and rejoice with trembling.
Kiss the Son,
lest he be angry, and you perish in the way,
for his wrath is quickly kindled.
Blessed are all who take refuge in him. - Psalm 2:10-12
In that day the root of Jesse, who shall stand as a signal for the peoples—of him shall the nations inquire, and his resting place shall be glorious. - Isaiah 11:10
Praise the LORD, all nations! Extol him, all peoples! - Psalm 117:1
He has remembered his steadfast love and faithfulness to the house of Israel.
All the ends of the earth have seen the salvation of our God. - Psalm 98:3
(See also 2 Samuel 22:50, Psalm 18:49, and Psalm 66:4.)
To say that the mystery of the Church is the inclusion of the Gentiles in the covenant blessing of God is to oversimplify what is being said. It is the difference between meat and milk.
This mystery is that the Gentiles are fellow heirs, members of the same body, and partakers of the promise in Christ Jesus through the gospel. - Ephesians 3:6
The Gentiles are fellow heirs with Israel and members of the same body. Provision was made for gentile proselytes in the Old Testament, but according to Scripture there was a separation or barrier between Israel and the other nations.
While provision was made for Gentiles under the Mosaic Covenant, there was also a sense in which Gentiles were excluded from Israel. Circumcision was a sign of the Old Covenant and non-Israelites were known as the uncircumcision. For a non-Jew the only way I'm was to be circumcised and to live as a Jew.
The Temple Complex in Jerusalem contained an outer court that was known as the Court of the Gentiles. The Court of the Gentiles was a large, open area where non-Jews could pray, learn about Judaism, or conduct business related to the Temple. Gentiles were not permitted to go into the inner court area and doing so was punishable by death. This forbidden area was accessible to Jews only. There was a physical wall of separation that divided the inner court from the outer court. This shows us that without the provision made by God there is no access to God. Under the Old Covenant Jews had access to God through their system of Ordinances and Sacrifices.
With this context in mind, Paul writes:
But now in Christ Jesus you who once were far off have been brought near by the blood of Christ. For he himself is our peace, who has made us both one and has broken down in his flesh the dividing wall of hostility by abolishing the law of commandments expressed in ordinances, that he might create in himself one new man in place of the two, so making peace, and might reconcile us both to God in one body through the cross, thereby killing the hostility. And he came and preached peace to you who were far off and peace to those who were near. For through him we both have access in one Spirit to the Father. So then you are no longer strangers and aliens, but you are fellow citizens with the saints and members of the household of God… - Ephesians 2:13-19
There is a lot to unpack here but the main point to consider for now is that through the blood of Christ, who fulfilled the Law, Jews and Gentiles have been made one new man (the Body of Christ). In Christ we are citizens of the Kingdom of Heaven and members of the Household of God.
Elsewhere we read that we who are in Christ - both Jews and Gentiles - are a new creation (2 Corinthians 5:17). In the Body of Christ, the one new man, there is neither Jew nor Gentile (Galatians 3:28 NIV). When we are born again by the Spirit it abolishes who we are according to the flesh.
All who are born again are members of the same body. This collective entity forms the corporate Body of the Messiah, and as we saw previously Jesus is the Head of that Body.
For just as the body is one and has many members, and all the members of the body, though many, are one body, so it is with Christ. For in one Spirit we were all baptized into one body—Jews or Greeks, slaves or free—and all were made to drink of one Spirit. - 1 Corinthians 12:12-13
Now we are beginning to touch the fringes of the great mystery that was made known to Paul.
The Church was not Plan B for the Godhead, it was conceived in the eternal purposes of God before the foundation of the world (Ephesians 3:11, Ephesians 1:4).
What most Christians know is that Jesus died for our sins so that we can go to Heaven. Of course we will praise God for all eternity for this reality, but few believers realize this was not God’s final goal but rather a means to a greater end. In Genesis Chapters 1-3 we see that God made man in His image (Genesis 1:27), He made man to have dominion (Genesis 1:28), and He made man to have fellowship with Him (Genesis 3:8-10). Psalm 8:5 tells us that God made man to crown him with glory and honor. When Adam and Eve fell in the garden, they were spiritually separated from God, they were mired in sin, and covered in shame. In short, man failed to be crowned with glory and honor. The Cross was the first step in remedying this fall from grace.
Christ died for our sins so that:
our fellowship with God could be restored
so that our image-bearing status could be repaired
so we could share in the glory of the Messiah
so we could receive an inheritance as royal sons and daughters of the King and co-heirs with Christ
so that we could be made partakers of His very Divine Nature
So that we could rule and reign with Him
In Christ we have been adopted into the household of God, blessed with every spiritual blessing in the heavenlies in Christ, and we have an inheritance as heirs with Christ. The forgiveness of sins was remedial. Justification, being declared in right standing before the Throne of God through the righteousness of Christ, is the starting point, not the end. We treat salvation as fire insurance to keep us out of hell but it is so much more than that. Sadly, far too many Christians fail to press on beyond the first few steps of the race.
The conquest of Canaan in the Book of Joshua is a picture of the redeemed obtaining their inheritance. The Promised Land does not represent going to Heaven as many people believe, it represents our Spiritual Inheritance. Our eternal inheritance is not something that is automatically received by default, it has to be obtained through Spiritual Warfare (see Ephesians 6). We must overcome. If we do not, we will forfeit what is rightfully ours. The Bible verses many take as evidence that salvation in Christ can be lost are actually talking about inheritance being lost or forfeited. An entire generation of Israelites died out wandering in the wilderness, failing to ever enter into the land flowing with milk and honey. So too will many Christians enter into eternity not having obtained the reward that could have been theirs.
Although the topic at hand is the Church, we must now take some time to more fully develop this idea of Inheritance and Reward. By doing so we may gain a greater understanding of the eternal destiny and high calling of the Body of Christ.
(1) Strong's G602 - apokalypsis
(2) Strong's G3466 - mystērion
(3) Example Joseph B. Rotherham's Emphasized Bible https://studybible.info/Rotherham/Ephesians%203