The Christian Ecclesia (Church) is infallible and is the dispenser of all the Graces of the Holy Spirit of God. The Ecclesia is a Divine Institution composed of a Divine Body. The Divine Body is Holy because of being that of Christ, Who is our Immortal and Living God. The Head of the Ecclesia is Jesus Christ and the Ecclesia is kept in the Truth by the Holy Spirit through the Agape of the Father and is administered by Christ.
In contrast, Satan has established a set of false "ecclesia" like entities that seek to mimic Christ's Ecclesia. These entities, these false "ecclesia" like organizations are of the world but immitate the work of Christ and act as a decoy to the Truth of the Holy Gospel, for they preach a foreign "gospel". This is where denominationalism sits. Denominationalism is foreign to the Body of Christ and therefore is not a part of the Ecclesia of Christ Jesus.
Consequently, denominational "christian" organizations are headed by unholy men and women who impurely operate a panoply of false religions that masquerade as Christian ministries teaching their unique versions of the "christian faith". Some of these denominations appear to be genuine, appear to be of the genuine Christian Faith in every manner. However, these organizations are on the outside and are religions manifested from false teachers of heresy. They don't want their flock to study the work of the Holy Spirit in the genuine Christian Ecclesia. Some don't mind referring to part of this work, but in the same breath, they are quick to demarcate current "christianity" from that of those "apostolic" times. Others emphasize "spiritual sorcery" and "new age" thought making religion a self-help gymnasium of spiritual growth "opportunities" with which to "earn salvation" and a "place in the Kingdom to come". But the most insidious of all these false religions is the one which mimics the Christian Ecclesia in every detail except its Oneness, its Holiness, and its Apostolicity. Its "spirit" is the antichrist because it does not dispense agape, grace, peace, or healing. Instead, it destroys and maimes its members and swallows up all those who attempt its overthrow. This most insidious of all false religions is drunk with the Blood of the Saints and its chalice is full of the abominations and filthiness of spiritual fornication which it presently and has always committed with the kings of this world. This particular false religion sits on seven mountains and is easily identified as coming from the City of Rome. (Revelation Chapter 17, entire chapter)
Indeed, this mother of all harlots is the root of all denominationalism. There is therefore a beast with seven heads and ten horns who is the source of lies, destruction, death, and darkness. This organization holds itself forth as the defacto standard of religious "truth" and makes the claim that it is the only "pathway to salvation". Yet in this organization one cannot find the choirs of the Angels, the communion of the Saints, and the Glory of God expressed in Agape. It is the father of all lies and its identity is exposed by the number of its horns: 10 horns of deception and world domination. The beast of 7 heads and 10 horns is the "king" of darkness who attracts all men who love darkness rather than the Supernal Light. Why would anyone want to remain with this beast, the loser of big proportions? We are called to illumination and righteousness. We are commanded to make disciples of all Nations, baptizing them into the name of the Father and of the Son and of the Holy Spirit. What part of this command do we not understand? Do we respect Christ our Lord or not? Why do we look on and see people baptized into the name of the beast instead of in Christ? Why do we see the preaching of multiple "gospels" foreign to the One Gospel of Christ? It is time to dispel these false doctrines and cleave to the Holy (Pure and Clean) Teachings of Christ Jesus our Lord. It is time to root out all the wolves among us and place those wolves in exile until they repent.
We call all God-loving and God-fearing members of these denominations to come out of these false "ecclesia"-like organizations and become illumined in the undivided Holy Ecclesia of Jesus Christ. In this manner, each person answering this call will have been enabled to illumine their friends and relatives who still are members of this monolithic one world religion.
Study the teachings of your particular denomination. Then, one by one, compare them to the Holy Gospel, and the Seven Ecumenical Councils of the Holy Ecclesia of Jesus Christ. Wherever the doctrines deviate, you have identified the heresy which is prevalent in your denomination's doctrinal teachings. If your research confirms that your denomination is in heresy, then you would decide to join the Holy Universal (Catholic) Ecclesia of Christ Jesus as an individual desiring to renounce all the heresies you had followed. Then you become a member of the genuine Holy Body of Christ.
Ecumenism is also the grandest of all Heresies: the Heresy of Heresies. It stands for the principle that the Holy Undivided Ecclesia should, with syncretism, join with denominational "christianity" and push all theological differences under the rug and agree not to agree on religious doctrine. Far from bringing peace into the equation, ecumenism would tear apart the flock at its roots and cause utter annihilation of the "faith". As one cannot join opposites, there is no way to join true and false statements in one lump and call them all true! If 2 + 2 = 4 is taken as true and at the same time 2 + 2 = 5 is erroneously taken as true, then how can such absurdities prevail? Likewise with the Truths given us by Christ. Can the Truths given by Christ be intermingled with the false teachings of evil and darkness? Certainly not!