The principal is that Christians worship One God "Allah". The name "Nasraniya" refers to the religion that Allah Almighty sent down upon 'Isa (Jesus) (peace be upon him) and its Book is called the Bible. The disciples of this religion are called "al-Nasara" in reference to the city of "al-Nasra" in Palestine or it is an attribute to the disciples of 'Isa (peace be upon him). This name "al-Nasara" was firstly attributed to the ones who believed and was soon generally given to the majority.
Christianity has soon spread among nations and the number of christians shortly increased after the ascend of 'Isa (peace be upon him). As we have mentioned before, Christians principally believe in One God, the Prophtes of the people of Isreal who preceded 'Isa (peace be upon him) and the Books revealed to them.
· Christianity and the concept of 'Trinity':
Christians deviated from monotheistic Christianity and came up with a mysterious doctrine in the 4th centurey which is still a source of controversy among Christians. This doctrine is known as 'Trinity' which simply states that God is three persons in one Godhead. The three are: God the Father, God the son and God the Holy Spirit.
There is a consensus among Christians that God is Divine in iself and three according to the concept of Aqnumiya (i.e. Hyposasis). The first referes to God himself while the second refers to His attributes "Sifat" such as existance, knowledge and life. They refer to life and the self of God as "the Holy spirit", they refer to God as "Divine" or "al-Lahoot" and man as "al-Nasoot".
· How was trinity introduced to Christianity?
The formulation of the doctrine of trinity is dated back to the time of the Roman Emperor Constantine. Constantine gathered great number of Bishops, 318 or 317, in Niqiya where Arius, the Bishop, stood against Constantine and declared the monothiesm of God, the Creator, and Jesus is His Prophet. Thereupon, they contradicted him and formulated a doctrine from their own invention derived it from their distorted books and named it "al-Amana" "The Nicene creed". Whoever disbelieves in this invented doctrine will get out of Christianity.
Al-Shahristani stated this doctrine "The Nicene Creed" in his book "al-Milal wa al-Niha": "We believe in one God the Father Almighty, Maker of heaven and earth, and of all things visible and invisible. And in one Lord Jesus Christ, the only-begotten Son of God, begotten of the Father before all worlds, God of God, Light of Light, Very God of Very God, begotten, not made, being of one substance with the Father by whom all things were made; who for us men, and for our salvation, came down from heaven, and was incarnate by the Holy Spirit of the Virgin Mary, and was made man, and was crucified also for us under Pontius Pilate. He suffered and was buried, and the third day he rose again according to the Scriptures, and ascended into heaven, and sitteth on the right hand of the Father. And he shall come again with glory to judge both the quick and the dead, whose kingdom shall have no end."
Then they added: "And we believe in the Holy Spirit, the Lord and Giver of Life, who proceedeth from the Father." They severly punished anyone who added or omitted any of this doctrine.
God according to the Christian Anthanasian creed: "Whosoever will be saved, before all things it is necessary that he hold the catholic faith: that we worship one God in Trinity, For there is one person of the Father, another of the Son, and another of the Holy Spirit. But the Godhead of the Father, of the Son, and of the Holy Spirit is all one, the glory equal, the majesty coeternal."
To conclude, trinity is a fasle illogical doctrine and contradicts the Oneness of Allah Almighty. Not only this, but it also contradicts the true faith for which Jesus (peace be upon him) called for.