Many good people teach that the Old Testament is a shadow and a type for our New Testament. There is no weight put in the gospel we see in the Old Testament. We primarily look to the New Testament to be our gospel and leave the Old Testament as something as a side dish or fine wine that brings out the flavor of our gospel.
The New Testament however does not look at itself as the gospel but strangely it looks to the Old Testament as the gospel. Hebrews comes right out and says this. Call it Paul, call it Apollos or somebody else, the writer of Hebrews understood and expected his readers to understand the gospel we hope in was also preached to those at Mt. Sinai.
For unto us was the gospel preached, as well as unto them: but the word preached did not profit them, not being mixed with faith in them that heard it.
Of course we know Peter didn’t preach from the New Testament on the day of Pentecost but he preached the gospel from the Old Testament, our gospel, as fulfilled in part through Christ.
To fast forward for expediency, we look at Paul in the last chapter of Acts preaching our gospel from the Law of Moses and the prophets, not from some New Testament scraps and parchments. He did it from the dry and dusty Old Testament.
And when they had appointed him a day, there came many to him into his lodging; to whom he expounded and testified the kingdom of God, persuading them concerning Jesus, both out of the law of Moses, and out of the prophets, from morning till evening.
So with this understanding The gospel According to the Gospel advocates that part of the gospel that Paul was teaching in Rome, in the last chapter of Acts from the writings of Moses, is exactly what he has given us in the book of Romans.
Paul, speaking from Moses’ books lets us know that God imputed Abraham righteousness and the seal of this righteousness is circumcision.
And he received the sign of circumcision, a seal of the righteousness of the faith which he had yet being uncircumcised: that he might be the father of all them that believe, though they be not circumcised; that righteousness might be imputed unto them also:
The consistency of the Old Testament gospel is found in his other writings as well. Paul teaches us gentiles, that we are now included in this gospel found in the writings of Moses. Through Christ we are partakers in the one blessing given to Abraham through which we can receive the Holy Spirit. This one blessing is the blessing of circumcision, imputed righteousness. To assume we can receive the Holy Spirit through any other means other than having our sins not being held against us, to assume that Christ came for some more pressing purpose than to take the sins of the word upon Himself would be preposterous. There is only one blessing that Paul teaches we gentiles can have with Abraham and this is imputed righteousness.
That the blessing of Abraham might come on the Gentiles through Jesus Christ; that we might receive the promise of the Spirit through faith.
This is why we see the consistency of the gospel Paul preached from the books of Moses when he says that Christ was a minister of circumcision. Some want to translate this to mean minister to the Jews and not minister of circumcision, because they see circumcision as a seal of Jewishness, not as a seal of righteousness as Paul taught from the gospel of the Old Testament. This translation is in direct contrast to what Paul has already taught us in earlier chapters of Romans. Circumcision is a seal of imputed righteousness.
Now I say that Jesus Christ was a minister of the circumcision for the (1)truth of God, to (2)confirm the promises made unto the fathers: And that the (3)Gentiles might glorify God for his mercy; as it is written, For this cause I will confess to thee among the Gentiles, and sing unto thy name.
Jesus being a minister of circumcision confirms what Paul said earlier, that circumcision is a seal of imputed righteousness. Jesus is in the business of paying for sins and imputing righteousness. This fact He is a minister of circumcision does three things. First of all it confirms the consistency of our gospel found in the Old Testament as truthful for which we can have certainty to put our hope in.
Secondly, Jesus being the minister of circumcision confirms the core of the message of our Old Testament gospel, this being Christ died to save sinners. By confirming the promise to those fathers of the Old Testament which was given by an everlasting covenant, Christ affirms circumcision as a seal of righteousness. Christ affirms circumcision by fulfilling the payment for sin, to which the fathers long to see in their day. Christ is the fulfillment of circumcision, that being imputed righteousness.
Thirdly, not only is Christ the fulfillment of circumcision to the Jew but, as Paul states in his gospel, we gentiles are now included in the blessing of Abraham. We gentiles too will glorify God for His mercies towards us through Christ being a minister of circumcision unto us. We too through Christ share in the imputed righteousness of circumcision even though we are uncircumcised. We gentiles now through Christ share in the blessing of Abraham concerning circumcision. For God has circumcised our hearts.
Isn’t it a wonderful thing how the true gospel of scripture flows so beautifully? Isn’t it wonderful to know our gospel is all of scripture? But understanding this, how do you think the realization of circumcision being a seal of imputed righteousness affects our gospel? It does in many ways concerning election, eternal security, faith, backsliding and all other issues pertaining to the Christian faith. But are you ready for the gospel the church refuses to believe?
The people of Israel were given the seal of imputed righteousness, just as we have, but what did they do with it? Did they have eternal security? What can we learn from their election? What were the consequences of their backsliding? How differently does the New Testament consider their faith from what we profess today? Remembering we share in the gospel they had, the blessing they had, and are grafted into their promises as an unnatural branch. We have nothing to stand alone on in our New Testament, outside of the gospel we find in the Old Testament. But are you ready for the gospel the church refuses to believe?
 Acts 28:23
 Romans 4:11
 Galatians 3:14
 Romans 15:8-9