All of the churches share this error - the most ancient and the most recent.
Jesus prayed this request in the hearing of His disciples: "I do not ask on behalf of these alone, but for those also who believe in Me through their word; that they may all be one; even as You, Father, are in Me and I in You, that they also may be in Us, so that the world may believe that You sent Me. The glory which You have given Me I have given to them, that they may be one, just as We are one; I in them and You in Me, that they may be perfected in unity, so that the world may know that You sent Me and loved them, even as You have loved Me. Father, I desire that they also, whom You have given Me be with Me where I am, so that they may see My glory which You have given Me, for You loved Me before the foundation of the world.
Paul wrote to the Corinthian believers, "Now I exhort you, brothers, by the name of our Lord Jesus Christ, that you all agree and that there be no divisions among you, but that you be made complete in the same mind and in the same judgment."
He wrote to the "Ephesian" believers, "I, the prisoner in the Lord, exhort you to walk worthy of the calling with which you have been called, with all humility and gentleness with patience, bearing with one another in love, being diligent to keep the unity of the Spirit in the bond of peace. There is one body and one Spirit, just as also you were called in one hope of your calling; one Lord, one faith, one baptism; one God and Father of all who is over all and through all and in all...And He Himself gave some as apostles, and some as prophets, and some as good-message tellers, and some as pastors and teachers, for the equipping of the holy ones for the work of service, to the building up of the body of Christ, until we all attain to the unity of the faith, and of the full knowledge of the Son of God, to a mature man, to the measure of the stature which belongs to the fullness of Christ".
The latest conservative count of the number of denominations in the world is between 9,000 and 12,000. This large range of numbers accounts for the fact that there are approximately two denominations added to the number per day each year. This subdividing of the one body of Christ into thousands of parties (separate bodies of Christ) is not of God. This mindset is devoid of the Spirit, and quenches His Holy Spirit, bringing great dishonor to Him! The Scriptures quoted above were what was required in the last days in the power of the Holy Spirit, not even to mention what is required in this Day Age.
Each subdivided group of the one body of Christ actually thinks this state of affairs is spiritual! They accept this as settled fact and seek the lowest common denominators in their "fellowship" experience with one another, if they even have one. This God dishonoring belief system is grounded in the mind of the flesh, the mind of mere babes, the mind of reckless people. And yes, most of these denominations, if not all of them, falsely think they are the ones in God's Holy Spirit about how He rules among His people through His Son, and that the rest are out of step with Him from one degree to another; from one state of grace to another state of damnation as determined by the denominational factions. The people who are disciples of the multitudes of denominations verify that these divisive characteristics are fully established. For they are revealed in each person's lack of seeking full unity with others outside of their denomination. Some do not even seek unity within their subgroup.
In truth, God has already revealed what is blessed and what is condemned though His word, the Scriptures. He has already revealed where the true unity of the body of Christ is. It is all far above earthly disciples of division. It is in His Kingdom manifested upon His spiritual Mount Zion and within His city, Heavenly Jerusalem. Here the glory and love of Jesus are manifested. Here the unity of the Holy Spirit in the bond of peace is fulfilled and made known. Here God is All in all!
Jesus Christ is the author and perfecter of believing Jahveh!
Why do you not believe His request to the Father and His exhortation through His apostle?
Jesus Christ is the author and perfecter of believing Jahveh!