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
Ephesians 3:3 says that 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) God revealed His sacred secret to Paul.
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 for us then is that God only reveals certain spiritual knowledge to those who are born again - to those who are initiated into the Kingdom of Heaven as it were.
As stated earlier, certain things cannot be known unless they are revealed to us spiritually. For example, Jesus the Eternal Son reveals or makes known the Father:
…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
And:
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)
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 unveiled to him. Without that mystery being given, Paul could not have known it (and by extension neither could we have).
So then, 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
From this many commentators 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. It was known in the Old Testament that God would bless the Gentiles and the Gentile Nations. Provision was made for Gentiles in the Hebrew Bible. 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 gentile Harlot from Jericho - along with 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). Additionally they could eat and be filled from the tithe of the produce during the harvest season in Israel (Deuteronomy 14:28-29).
Furthermore, 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 in 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 literally 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. Provision was made for Gentiles in one sense yet the Mosaic Covenant served as a barrier as it were between Israel and the Gentile Nations.
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 our purposes now is that through the blood of Christ, who fulfilled the Law of Moses (Matthew 5:17), Jews and Gentiles have been made one new man and one body. This one new man is the Body of Christ - the Church. All who are in Christ are citizens of the Kingdom of Heaven and members of the Household of God.
Let us return to Ephesians 3:6:
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.
I would venture to guess that there is an aspect of the Gospel that the overwhelming majority of Christians do not understand because they have never been taught it. They understand that Jesus died for their sins, but they do not understand that they also died with Christ at the Cross.
The first five chapters of Romans deal with Christ dying for us (see Romans 3:23, 5:8). Romans 6 reveals the above-mentioned second aspect of Christ’s work at Calvary:
How can we who died to sin still live in it? Do you not know that all of us who have been baptized into Christ Jesus were baptized into his death? We were buried therefore with him by baptism into death, in order that, just as Christ was raised from the dead by the glory of the Father, we too might walk in newness of life. - Romans 6:2-4
Based on this some might spiritualize this and make it more allegory than reality. But Romans 6:6-8 eliminates any such idea:
We know that our old self (literally the old man) was crucified with him in order that the body of sin might be brought to nothing, so that we would no longer be enslaved to sin. For one who has died has been set free from sin. Now if we have died with Christ, we believe that we will also live with him.
The old man was crucified and died (past tense) with Crist at the cross. So what does that mean? What is the old man?
Romans 5:12-19 explains this. Adam was created sinless but he sinned in the Garden of Eden as described in the Book of Genesis. Adam’s sin was propagated to all of his offspring. Because of sin we all die physically.
…sin came into the world through one man (Adam), and death
through sin - Romans 5:12
Many of us can recite 2 Corinthians 5:17, but have we grasped what is being said?
Therefore, if anyone is in Christ, he is a new creation. The old has
passed away; behold, the new has come.
The phrase new creation can literally be rendered new creature. Before we are born again, we are ‘in Adam’ dead in the trespasses and sin (Ephesians 2:1). All have sinned and fallen short of the glory of God (Romans 3:23).
When we are born again we are transferred from Adam to Christ. We move from being ‘in Adam’ to being ‘in Christ’ - a phrase that we see over and over in the New Testament.
Romans 6:11 is the the application, the payoff if you will:
So you also must consider yourselves dead to sin and alive to God in Christ Jesus.
We must consider ourselves dead to who we are in Adam and alive in Christ.
I have been crucified with Christ. It is no longer I who live, but Christ who lives in me. - Galatians 2:20
We no longer regard ourselves or each other according to the flesh - that is, who we are in Adam (2 Corinthians 5:16). We are to regard each other according to who the Bible says we are in Christ (which Paul spells out in the first three chapters of Ephesians).
What I have just explained to you is the basis for sanctification by the way. We spend our time reading well-intentioned Christian books on self-improvement and trying to do better. We don’t realize that this is a fool’s errand. We are spinning our wheels and wasting our time. God is not asking us to do better. He is calling us to die.
We admit to God that we are weak and we ask Him for strength. But that implies that we have some strength in us, something of merit. But who we are in Adam is irreparably broken and beyond improvement. Here is a quote from The Green Letters (highly recommended) that concisely makes this point:
…God consigns the old fallen Adam-life to the cross, and has nothing to say to it. God deals with all believers on the ground - ‘In Christ you died.’(4)
To be alive in Christ we must be dead to who we are in Adam.
There are two aspects of the Gospel and the finished work of Christ, but most Christians only ever hear about the first. The blood of Christ deals with our sin. The cross of Christ deals with the sinner. In Adam we are sinners. We have a terminal sin nature. Who we are in Adam was taken into death with Christ on the cross. The work is finished but we must appropriate it on an ongoing basis by reckoning our old nature to be dead with Christ on the cross.
In Christ, where we find new resurrection life, there is neither Jew nor Gentile. There is one new man. This means that the resurrected Christ is neither Jew nor Gentile. We know this because the Head and Body are one. We can't be one with the Head and yet be of a different nature than the Head. This means that the term Messianic Jew really only applies in human terms but not in the ultimate, eternal sense. The implications of this are too vast to deal with here. I only bring it up to highlight that this reality is more radical than we might initially realize. It's a realization and a reality that really shatters prevailing paradigms.
To summarize, the mystery that was revealed to Paul is that the Lord Jesus
create(d) in Himself one new man in place of the two (Jews and Gentiles), so making peace, (that He) might reconcile us both to God in one body…
How?
through the cross, thereby killing the hostility. - Ephesians 2:16
Christ died for us. We died with Him.
Works Cited
(1) Strong's G602 - apokalypsis
(2) Strong's G3466 - mystērion
(3) Example Joseph B. Rotherham's Emphasized Bible https://studybible.info/Rotherham/Ephesians%203
(4) Miles J. Stanford, The Green Letters Principles of Spiritual Growth, pg 52, Miles J. Stanford, 1975