The division of the Churches occurred as a result of human sin; the Lord Jesus Christ Himself created one Church and specifically prayed for its unity.

At first, differences (dissensions, as the Bible calls this phenomenon) were perceived as the richness of the Church. But at the end of the first millennium, the mutual alienation of the Churches of the West and the East led to the fact that Christians of the two parts of the Roman Empire ceased to understand each other and, what is most terrible, lost the sense of the importance of unity.

Over the course of several centuries (from the 6th to the mid-11th) differences in the way of thinking and acting of the West and the East did not prevent unity; however, several times during this period, a schism between the Churches occurred due to the political pressure of the state authorities of the West and the East. Finally, by the 11th century, against the background of mutual misunderstanding, this political schism in 1054 became final. It lasted 910 years and was overcome in 1964 at a meeting between Pope Paul VI and the Patriarch of Constantinople Athenagoras I, although reasons for mutual reproaches and dissatisfaction continue to arise to this day.

In addition, in the depths of the Western Church by the 16th century, dissatisfaction with its own shortcomings had matured, which led to the emergence of Protestantism, which subsequently divided into countless branches.

All this was, we repeat, caused by purely human reasons, or rather — sins. In essence, the matter lies in our inability to love and accept those who differ from us. Gradually, the main motive for mutual reproaches between the Churches became a lack of faith and a desire to justify one's own spiritual tradition not by the fact that people find Christ in it, but by its advantages over others.

Division and its consequences are the foremost sin of Christians. How did it become possible? Like any sin — because God respects our freedom. In the Church, in accordance with its nature, two principles operate — God's will, good and perfect, leading the Church to holiness and unity, and human nature, fluctuating between obedience to God and its own sins. If the second principle did not exist, there would be no division, but then it would not be a Church, but a concentration camp, and there would be no place for us all in it. After all, the fact that God accepts us while we are still sinners is our only hope for salvation.

To whom, to which Church a Christian (a person who has come to believe in Christ) should turn so as not to make a wrong step, is determined by each person in prayer. In principle, there is a cultural community of people, which is largely formed under the influence of certain confessions. That is why in every country one can distinguish a Church close to the majority. In Russia, this is undoubtedly the Russian Orthodox Church. However, each person's path to God is unique, and the Lord calls different people into different parts of the Church. The point, actually, is not in a right or wrong step, but in where Christ wants to grant an encounter with Himself specifically to this person.

At the same time, it is important to distinguish parts of the Church from countless sects and so-called "new religious movements." The simplest criterion is the origin of the Church from the apostles and its connection with global Christianity. In church language, this is called apostolic succession. On the territory of our country, apostolic succession, besides the ROC, is also possessed by the Roman Catholic and Armenian Apostolic Churches.

Understanding the versions of Protestantism is not so simple; here there are no clear criteria of ecclesiality. In addition, it is important to keep this in mind: if a person was baptized in childhood (in Russia this almost always means Orthodoxy), then there is no point in changing confession without very serious reasons, unless they were baptized in some dubious sect... It is much more important to find a specific community for oneself within one's own confession; after all, within every "normal" Church there is a fairly wide diversity.

The main thing is very simple: you need to seek Christ Himself, and He will show you the Church...

To us, just as to you, the explanation you provide seems strange. The Apostle Paul, as far as can be understood, is speaking about the following. He who unites himself with a prostitute is one with her in body. Conversely, the apostle writes, he who unites himself with the Lord is one with Him in spirit. The apostle uses the verb kollao in both cases, literally meaning "to glue, to cleave, to join." He is appealing to the imagery conveyed in the Book of Genesis by the words "and a man shall cleave to his wife, and they shall become one flesh." This is where the verb "cleave" comes from.

Just as the words "they shall become one flesh" do not imply merging, so in the second case the bold imagery of the apostle does not imply the merging of the human spirit with God. On the contrary, the apostle is faithful to the tradition of the Old Testament, which uses marriage as an image of the relationship with God, where there is essential unity, the closest of bonds, while preserving the distinction of persons, where the persons do not merge into one, but become inextricably together. In the union of people "in one spirit with the Lord" there is similarly no merging, the essential distinction of individualities similarly remains, but the closeness of this unity is such that it is impossible to imagine one without the Other.

Thus, it refers to what the theology of the first millennium (so-called patristic theology) termed "theosis" (deification). The Lord Jesus Christ spoke of this: "that all of them may be one, Father, just as you are in me and I am in you, may they also be one in us." This is the entering of people into the mystery of the love of the Trinity, such love that overcomes difference and unites without violating freedom and individuality. Just as the Father and the Son are one, so too can a person who has cleaved to the Lord be one with God and other people. Strictly speaking, this unity without merging is paradoxical; human thought knows no examples of it other than the Trinity. And such union with God is precisely the ultimate goal of our lives.

Therefore, the Apostle Paul is speaking in a somewhat unusual manner about the covenant (union) with God, to which humanity is called.

Arianism considered the Son of God, Christ, not equal to the Father. Arius and his followers believed that the Son was begotten by the Father, but a) did not exist before He was begotten (that is, He is not eternal); b) is not without beginning; c) is not equal to the Father and d) is not consubstantial with the Father, i.e., He has a different essence (nature) and, therefore, is not fully God. Practically, this led to the Arians considering the Son to be a created being. After the defeat of the Arians at the Council of Nicaea in 325 AD, various factions began to develop within Arianism, differing in some details. However, they all held to a common view that disagreed with the Christian understanding of the Triune God and the Incarnation of the Son of God. One way or another, these movements can be classified into the category of anti-paradoxical: they did not accept the paradoxical description of God, mainly that God is one in the Trinity and Christ is fully God and fully man.

Christians, in their polemics against the Arians, rely on such words of Holy Scripture as "I and the Father are one" ( 17:21) and "that they all may be one, as You, Father, are in Me, and I in You" ( 10:30), as well as "[in Christ] dwells all the fullness of the Godhead bodily" ( 2:9) and a whole series of others. Furthermore, the Nicene and subsequent councils proceeded from the so-called soteriological criterion: in order for the salvation of humanity to be genuine, it is necessary that God Himself fully become man and share with us both our nature and our destiny, so that we might have the opportunity to share His life with Him.