The main Christian doctrine is the understanding of God as the Holy Trinity - the Father and the Son and the Holy Spirit. People who profess God this way are called Trinitarians.
Indeed, Christians are only those who profess the trinity of the deity. There are three branches of Christianity: Orthodoxy, Catholicism and Protestantism. In all these denominations, God is the Trinity: the Father, the Son, and the Holy Spirit. Although in the Trinitarian theology there may be a difference. For example, the Orthodox say that the Holy Spirit comes from God the Father, and Catholics add that the origin of the third incarnation of the Holy Trinity comes from the Father and the Son. This is the so-called “filioque” insert, which at one time (even before the separation of the Churches in 1054) was added to the Nicene Tsaregradsky Creed.
In addition, we can mention the so-called pre-Chalcedonian churches, for example, the Coptic church, the Armenian church and several others that did not accept the decree of the IV Chalcedon Ecumenical Council. These Christians are neither Orthodox nor Catholic, nor do they belong to Protestants. The dogma of the trinity of deity in the pre-Chalcedonian Churches is supported. However, there is some discrepancy with orthodox Christianity regarding natures in Jesus Christ. So, at the IV Ecumenical Council, the dogma was drawn up that there are two natures in Christ - divine and human. The council was called upon over disputes at the expense of the human being in Christ. Opponents of the Council of Chalcedon claimed that in Christ there is only one nature. Dohalkidon churches still have this opinion.
Now it is worth mentioning the sects, some of which consider themselves Christian. For example, Jehovah's Witnesses (natives of Protestantism, a totalitarian sect of the Western type) do not adhere to trinitarian views on the essence of the deity. That is why this organization is non-Christian. In the same categories one can speak of other sectarians and representatives of various currents of pseudo-Christianity.
Thus, it turns out that Christians in the full sense of the word are those who profess the trinity of the deity. He who is not a Trinitarian (does not profess the trinity of God) cannot be called a Christian in the full sense.
