There is only One Church and Eternal Covenant!
"And these all, having obtained a good report through faith, received not the promise: God having provided some better thing for us, that they without us should not be made perfect." Hebrews 11:39,40
Chapter eleven of Hebrews lists the prominent saints of the Old Testament. It begins by defining faith as the "substance of things hoped for, the evidence of things not seen." Then, starting with Abel, who offered a more excellent sacrifice than Cain, and ending with the martyrs of the Old Testament, the chapter includes brief bios of the heroes of faith in the Old Testament. People like Enoch, Noah, Abraham, Moses, Jephthah, Rahab, Samuel, Gideon and others are mentioned by name, but other very great saints like Job, Ruth, Elijah and Elisha, Isaiah and Daniel are not mentioned except indirectly.
But all of these gain a "good report" through faith: They were accepted of God on account of their faith and were perfected, obtained eternal life and enjoy eternal bliss in the presence of God forever, for He is not God of the dead but of the living, as Jesus said [Matt. 22:32]. There has never been any other way to please God than by faith, for "without faith it is impossible to please him: for he that cometh to God must believe that he is, and that he is a rewarder of them that diligently seek him."
But none of these glorious saints, now in heaven, received the promise. What is the "promise" that they did not receive, that better thing that "we" have that these Old Testament saints did not have? Many of them had the joy of salvation [Ps. 51:8-12], the promise of the world to come, great earthly blessings [Abraham and Job, for instance], and all of them had trials and testings. They suffered the reproach of Christ and drank of living water and living bread [1Cor 10]. They even had the blessings of the Holy Spirit in a measure [Is. 63:10,11; Neh. 9:10].
The difference is Jesus Christ. They did not have the full knowledge of the Lord Jesus, but only saw Him "afar off" by faith as Abraham did [John 8:56]. Their lack of knowledge and hearing and seeing the ministry of the Lord Jesus did not mean they were not perfected, for it is by faith in Christ that we find the perfection and all the fullness of the Godhead bodily. They had the gospel preached to them [Gal. 3:8, ], but it only profited those who believed [Heb. 4:2; Rom. 9:31,32]. Isaiah prophesied that the Spirit of God would be on Messiah to preach the gospel [Is. 61:1,2 with Luke 4:18]; Daniel also knew that Messiah would make an end of sins, reconcile for iniquity, bring in everlasting righteousness, and fulfill the prophecies [Daniel 9:24]. In fact, the first promise of the Bible concerning the Lord Jesus is in Genesis 3:15, when God told Eve that her seed would bruise the head of the serpent [mortally wound his power and authority over man because of sin and guilt [Heb. 2:14,15], and would himself be bruised in his heel by the serpent [Christ's kingdom, suffered a small set back, but triumphed over the devil by Christ's resurrection].
Moses saw only the hinder parts of God and could only reveal the backside of the Gospel, if you will. [Exodus 33:20-23]. Jesus, as the S0n of God, could see God face to face [2Cor 4:6] and we behold the glory of God in the face of Jesus Christ. This was withheld from the saints in the Old Testament, reserved until the coming of Christ and His manifestation to the world. But this did not prevent the believer in the Old Testament from having genuine faith and obtaining the perfection of faith that is found in Christ alone. Their faith was not inferior to ours, but their knowledge was.
The Church stands by faith, and falls by unbelief, just as Israel [Romans 11L20-18-23]. In fact, the church has a greater responsibility because she has been given greater knowledge. "If the word spoken by angels was steadfast, and every transgression and disobedience received a just recompense of reward; How shall we escape, if we neglect so great salvation; which at the first began to be spoken by the Lord, and was confirmed unto us by them that heard him.... [Heb. 2:2,3]" To whom much is given, much is required. those in Israel, because of her blessings, will receive greater judgment than Sodom, or Tyre, or Sidon who did not have such mighty works done of God.
Even more so, those of the Church who reject faith and repentance can expect greater wrath than Israel: "26 For if we sin wilfully after that we have received the knowledge of the truth, there remaineth no more sacrifice for sins, But a certain fearful looking for of judgment and fiery indignation, which shall devour the adversaries. He that despised Moses’ law died without mercy under two or three witnesses: Of how much sorer punishment, suppose ye, shall he be thought worthy, who hath trodden under foot the Son of God, and hath counted the blood of the covenant, wherewith he was sanctified, an unholy thing, and hath done despite unto the Spirit of grace [Heb. 10:26-29]?"
But those who do believe are one people in the Lord, perfected in Jesus Christ. It was God's plan, though hidden in mystery before the coming of the Lord Jesus to join those who believe in Christ, both Jew and Gentile to the perfected ones of the Old Testament, a holy people unto the Lord forever. Hence, the cross broke down the middle wall of partition between us, making us one in Christ. [Eph. 1:12ff] Those without hope, strangers from the promises, and "far off" from the covenants, are made nigh by the blood of Jesus, becoming one people and one family of God. [Eph. 1:19]. There is one redeemed people in the book of Revelation, redeemed from every kindred, tongue, people, and nation, by the "everlasting gospel." [Rev. 5:9]
It was revealed by the preaching of the Gospel in the book of Acts and in the Epistles, that what had been only known very dimly in the Old Testament was now being made clear: "Which in other ages was not made known unto the sons of men, as it is now revealed unto his holy apostles and prophets by the Spirit; That the Gentiles should be fellow heirs, and of the same body, and partakers of his promise in Christ by the gospel.... [Ephesians 3:5,6].
There is, therefore, One Lord, One Faith, One Baptism, One God and Father of all, who is above all, and through all, and in you all, but unto every one of us is given grace according to the measure of the gift of Christ [Eph 4:4-7]. Christ is all, in the Old Testament and in the New. In Christ we have "put on the new man, which is renewed in knowledge after the image of him that created him: Where there is neither Greek nor Jew, circumcision nor uncircumcision, Barbarian, Scythian, bond nor free: but Christ is all, and in all [Col. 3:10, 11]."
Amen and Amen. [Note: Scripture references are not designed to be "proof texts" but are pointers to passages and epistles that must be studied in their own context and the context of all of Scripture.]