As Salamu Alaykum,
I don't know what it is called, but I am really enjoying the "presence" of Allah through the study of Al Quran. Alhaduelah!
I hope to be able to concisely as possible explain some of the errors of Christianity which lead me to stop preaching, teaching, and pastoring in Christianity and begin to learn Islam.
In Christianity, each belief is called a doctrine. For those of you who are familiar with Anthropological Concepts, a doctrine is a Meme (a unit of belief which may be part of a Mega-Meme which could possibly be an entire political, economic, religious or social system).
The reason some Christians say that you must believe in the trinity to be a Christian is because during the reign of Constantine, Christianity had become the empires official religion. After much debate those who were considered by Constantine to be leaders in the Christian religion were given authority to decide what was an wasn't acceptable Christian Doctrines.
Which brings us to the two primary Theologies and Christologies of Christianity. Well, actually according to the most known proponent of Oneness Theology, the Theologian, David Bernard, from 150-258 three primary "schools" of Christianity developed along geographical lines: Asia Minor (Western Roman Empire) North Africa (where Latin was the primary language) and Alexandria, Egypt (a center for Hellenistic, Greek, Thought).
It is important to understand that the Christian Church was becoming not only a religious force but also a political influence.
During the time from 150-325 there are dozens of Theologians and Apologists who expounded interpretations of Christian Doctrine in Greek and Latin. Is it any wonder that there is so much disagreement, discord, and confusion about what is an is not authentic Christian beliefs. There are even groups such as The Nazarene Israelites who claim that all Christian Denominations teach doctrines that are contradictory to what Yeshua taught. And, my experience and study tells me that this is the case.
Eventually, The Roman Catholic Church became the authority on what was "Truth" and what was Heresy.
Around the time of Martin Luther, a protest against The Roman Catholic teachings which were in opposition to the same books of The Bible which they made Cannon. (which is where we have the start of Protestant Denominations) Each Protestant Denomination grew out of a division in a previous incarnation of "Christian Thought" based on a belief that the original group(s) failed to consider certain Scriptures. An excellent example of this is Oneness Pentecostals who believe that the only correct method of baptism is in accordance with Act 2:38: Then Peter said unto them, Repent, and be baptized every one of you in the name of Jesus Christ for the remission of sins, and ye shall receive the gift of the Holy Ghost. Act 8:16 (For as yet he was fallen upon none of them: only they were baptized in the name of the Lord Jesus.) Act 10:48 And he commanded them to be baptized in the name of the Lord. Then prayed they him to tarry certain days. And, Act 19:5 When they heard this, they were baptized in the name of the Lord Jesus.
While previous Pentecostal Denominations held to the Trinitarian Formula for baptism by emersion found in Mat 28:19 Go ye therefore, and teach all nations, baptizing them in the name of the Father, and of the Son, and of the Holy Ghost: (the phrase baptism by emersion is redundant since the word baptism means to submerse in water.
Of all the various denominations, The Christology held by The Jehovah Witness Organization founded by a man named Charles Taze Russell in the 19th Century comes closest to The Truth Revealed in Al Quran by Allah to The Prophet Muhammad (Sall Allahu 'Alayhi wa Sallem) through the angel Gabriel. However, it is not in total harmony and many teachings of The Jehovah Witness Organization miss the mark completely such as The Name of God being Jehovah when as Muslim know better than I there was know J in the Hebrew Language and consequently the assertion that the Hebrews were told to call Allah by the name Jehovah or that Yeshua's (PBUH) name was Jesus.
I hope this demonstrates to your friend just how much error exists in what goes by the name Christianity today and how even the Bible (due to translations, additions, subtractions, and rewording of translations) is very contradictory from one book to the next; and, consequently, has to rely on a practice which Itself condemns:
لِلْيُونَانِيِّ.*!
Rom*! 1:17*! لأَنْ*! فِيهِ*! مُعْلَنٌ*! بِرُّ*! اللهِ*! بِإِيمَانٍ*! لإِيمَانٍ*! كَمَا*! هُوَ*! مَكْتُوبٌ*!«أَمَّا*! الْبَارُّ*! فَبِالإِيمَانِ*! يَحْيَا*!».*!
Rom*! 1:18*! لأَنَّ*! غَضَبَ*! اللهِ*! مُعْلَنٌ*! مِنَ*! السَّمَاءِ*! عَلَى*! جَمِيعِ*! فُجُورِ*! النَّاسِ*! وَإِثْمِهِمِ*! الَّذِينَ*! يَحْجِزُونَ*! الْحَقَّ*! بِالإِثْمِ.*!
Rom*! 1:19*! إِذْ*! مَعْرِفَةُ*! اللهِ*! ظَاهِرَةٌ*! فِيهِمْ*! لأَنَّ*! اللهَ*! أَظْهَرَهَا*! لَهُمْ*!
Rom*! 1:20*! لأَنَّ*! مُنْذُ*! خَلْقِ*! الْعَالَمِ*! تُرَى*! أُمُورُهُ*! غَيْرُ*! الْمَنْظُورَةِ*! وَقُدْرَتُهُ*! السَّرْمَدِيَّةُ*! وَلاَهُوتُهُ*! مُدْرَكَةً*! بِالْمَصْنُوعَاتِ*! حَتَّى*! إِنَّهُمْ*! بِلاَ*! عُذْرٍ.*!
Rom*! 1:21*! لأَنَّهُمْ*! لَمَّا*! عَرَفُوا*! اللهَ*! لَمْ*! يُمَجِّدُوهُ*! أَوْ*! يَشْكُرُوهُ*! كَإِلَهٍ*! بَلْ*! حَمِقُوا*! فِي*! أَفْكَارِهِمْ*! وَأَظْلَمَ*! قَلْبُهُمُ*! الْغَبِيُّ.*!
Rom*! 1:22*! وَبَيْنَمَا*! هُمْ*! يَزْعُمُونَ*! أَنَّهُمْ*! حُكَمَاءُ*! صَارُوا*! جُهَلاَءَ*!
Rom*! 1:23*! وَأَبْدَلُوا*! مَجْدَ*! اللهِ*! الَّذِي*! لاَ*! يَفْنَى*! بِشِبْهِ*! صُورَةِ*! الإِنْسَانِ*! الَّذِي*! يَفْنَى*! وَالطُّيُورِ*! وَالدَّوَابِّ*! وَالزَّحَّافَاتِ.*!
Rom*! 1:24*! لِذَلِكَ*! أَسْلَمَهُمُ*! اللهُ*! أَيْضاً*! فِي*! شَهَوَاتِ*! قُلُوبِهِمْ*! إِلَى*! النَّجَاسَةِ*! لإِهَانَةِ*! أَجْسَادِهِمْ*! بَيْنَ*! ذَوَاتِهِمِ.*!
Any one with an English Bible can look up the English translation or find it on the web