The “keystone” is the one stone that is responsible for holding up the whole structure. It is that odd “v” shaped stone at the very top of a Roman stone arch that supported buildings, aqueducts, etc. The Apostle Paul refers to Christ as the “chief cornerstone” in Eph 2:20, such as a keystone (Gk. acrogoniaios, the top, uppermost part).

Paul tells us that he was determined only to know Jesus Christ according to “Him crucified.” 1Cor. 2:2 For I determined not to know any thing among you, save (except) Jesus Christ, and him crucified.  What does Paul mean by “know…Christ crucified”? By this Paul means to know Jesus as He now is from the cross forward. Have you ever noted that Paul never refers, even once, to anything of Jesus of Nazareth did before the cross – neither Jesus’ miracles nor what He said? Paul wrote the following along these lines of understanding.

2 Cor. 5:16 Wherefore henceforth know we no man after the flesh (humanity): yea, though we have known Christ after the flesh (humanity), yet now henceforth know we him no more.

Paul here is referring to Christ in His ministry as earthly “Jesus of Nazareth,” had come only to, and for, “the lost sheep of the house of Israel.” (Matt 15:24). Paul saw that by the cross, Jesus Christ’s form had changed; Jesus has died and resurrected to become “the Spirit” (2Cor 3:17a), “Spirit of life in Christ Jesus” (Rom 8:2), “the life-giving Spirit” (1Cor 15:45). Jesus is now available as the as “the Spirit of life”; available to be received by as many as would simply “receive Him” (John 1:12) by faith. Those recipients then are immediately placed into the invisible “church, which is His body” (Eph 1:22b-23a, 1Cor 12:13).

Paul was converted several years after the cross. Yet, Paul was the one to whom the ascended Christ first revealed the nuts and bolts of the effectual workings of His sacrifice at the cross; that is His blood, death and resurrection – to be taught to “the Gentiles” (Eph 3:1-5), as Paul wrote in his fourteen epistles. If we remove Paul’s writings from the Bible we have no understanding of the cross, the blood, the death and resurrection of the Lord as it applies effectually to us as the source of our blessed new lives that we possess “in Christ.”

By the account in early Acts we see that Peter, on the day of Pentecost and after never once mentions such items as forgiveness of sins, redemption, reconciliation, or any matters of the blood of Christ. He only preached the “gospel of the kingdom” to the “men of Israel” (Acts 2:22, 3:12, 5:35). I believe Peter knew nothing of the blood until he learned of it from Paul. Peter, the Apostle to “the circumcision (Jews),” in his latter years writes to the “scattered” of Israel (1Pet 1:1), revealing that he must have received his knowledge of Christ, and I suppose Christ’s blood, from Paul’s epistles. Peter, in 2Peter 3:15-16, commends the Jews to read “all of Paul’s epistles,” warning them that to “twist” Paul’s epistles leads to “destruction.”

This paper explains why it is that Paul would consider Jesus Christ crucified to be the focus of Paul’s gospel, which would “establish” the Christian.

Rom 16:25 now to him that is of power to stablish you according to my (Paul’s) gospel, and the preaching of Jesus Christ, according to the revelation of THE MYSTERY, which was kept secret since the world began,

“Stablish you” - Forgiveness of our sins by faith in Christ’s blood is a key first step to becoming “established” in Christ. The “establishing” of the believer comes from Paul’s “my gospel,” which includes the basis of our “assurance” of salvation and the forgiveness of all sins; that is through faith in the shed blood of Christ. With that “assurance,” we can have confidence in our relationship with God as our Father – we are established.

“The mystery” - Paul here defines the individual personal aspect of “the mystery” or “secret” gospel that the ascended Christ revealed to him, which is…the deposit of Spirit of Christ into the believer’s spirit.

Colossians 1:26-27 Even the mystery which hath been hid from ages and from generations, but now is made manifest to his saints (believers): ²⁷ To whom God would make known what is the riches of the glory of THIS MYSTERY among the Gentiles; which IS CHRIST IN YOU, the hope of glory:

We can only receive Christ into us with the cleansing of our sins that comes by faith in His shed blood.