While regarding themselves as monotheists...
While regarding themselves as monotheists, Trinitarian Christians believe in three Persons (or Essences) which are as follows: The Person of the Essence (God the Father); The Person of the Word (God the Son); and The Person of Life (God the Holy Spirit). According to them, each of these Persons completely possesses the truth of Godhood and all of these Persons are the same in the truth of Godhood. Thus, the truth of Godhood is one thing and for this reason, while God is One, He has three Persons.
In other words, the Essence of God (God the Father) has been reincarnated in the Person of the Word (Jesus Christ) through the Person of Life (God the Holy Spirit) and manifested in the image of Jesus Christ. For example, the Gospel According to St.
John begins with this passage: “In the beginning was the Word, and the Word was with God, and the Word was God… And the Word was made flesh, and dwelt among us.”[^6] And it is thus stated in the Epistle of Paul the Apostle which was written about ten years prior to the Gospel of John: “God who, in numerous Persons and different channels of the prophets, had talked with our fathers in the past, now talked with us these days through His Son.
He took him as the inheritor of all creatures and created the worlds through him.”[^7] In this regard, therefore, Trinitarian Christians believe in three things, thus: Christ is the Son of God; Christ is God (God the Reincarnate); and There are three Divine Essences and God is the third of them. Thee are doctrines which the Holy Qur’an has also mentioned and proscribed all of them as polytheistic beliefs.