First, men need to understand the nature of original sin. We all need to understand the hopelessness of achieving righteousness or perfection in ourselves. The Bible plainly condemns and shuts the mouths of all men in their attempts to fulfill the Covenant of Works. It doesn’t matter what system men find themselves, whether it be Buddhism or Islam or Judaism or Mormonism or Roman Catholicism, all systems of works, no matter how much grace may accompany one’s attempts will fail in utter defeat.
We must understand that it is Christ who has fulfilled the Covenant of works in our place as our Substitute and as our Representative. It was Christ and Christ alone who accomplished the salvation of all men from Adam to the present. And it is through faith alone in Him that brings a man into right relations with God. Therefore, we must call all men, both Jew and Gentile, to repentance and faith in Christ.
The New Covenant is the ultimate fulfillment of the purposes of God in saving a people for Himself in Christ. This covenant is not for one group of people over against another. But as the Apostle Paul rightly declares, Christ has made one new man by uniting both Jews and Gentiles in one Covenant. Gentiles do not merely share in New Covenant blessings. Instead the New Covenant everywhere teaches that Gentiles along with their Jewish brothers are full members with all of the New Covenant blessings. The entire Old Testament was a shadow or a type of what was to come in Christ.
The question that arises is the nature of the Law written upon the hearts. The New Covenant as described in Hebrews 8 never distinguishes between Jew and Gentile. The Law is written upon the hearts of all believers. There is no such thing as a “Carnal Christian” or a Gentile who only has forgiveness of sins but does not repent of his sins. The early church is made of believers and is considered the fulfillment of the promises of the Old Testament. This is where starting with the New Testament’s description of the New Covenant is vital. We must not allow inferences from the Old Testament override the plain teaching of the New Testament. Jesus and the Apostles must be allowed by the power of the Holy Spirit to be the final interpreters of the Old Testament and its promises. If they say it is fulfilled, then we ought not to challenge it but understand how it is fulfilled in a proper way.
The people of God in the church are not an afterthought or some secret not revealed to us in the Old Testament. The Church of Jesus Christ was always in the mind of God as typified throughout the Old Testament and fulfilled in the New. Although in this present age Christians struggle with their sin, she is always able to look to and find solace in her perfect Redeemer, who has bought her with His own blood. She presently possesses the forgiveness of sins and the righteousness of the Savior. She has been changed to be holy and to live holy in this world even with all of her abiding sin. Thanks be to God through Christ who has established His perfect Covenant that will never end and is completely unbreakable.