I believe my question was "why" all the different denominations. I never said what is unnecessary. However, to me the Gospel (meaning good news) is that God Almighty Maker of Heaven and Earth sent his only begotten Son to suffer a horrible death (the Passion of Christ movie is succinctly in showing that death) to save us unworthy and sinful misfits of creation and give us another chance!. That is my Gospel, spoken to mankind through the mouth of Jesus Christ our Savior.
As long as you understand that Christ’s sacrifice was voluntary and that Christ is God incarnate, that is to say, by being conceived in the womb of the Virgin Mary, that He put on our humanity while remaining fully God, and was fully God and fully man within out change, confusion, separation or division) the person of the Son and Word, coeternal and coequal with the unoriginate father (John 1:1-18), you just have correctly described the basic belief of all Nicene denominations including the Roman Catholic Church.
However because some people deny the Incarnation, the Trinity, the Crucifixion (Docetists were an ancient and vast heresy the members of whom denied Christ had physical flesh at all, whereas Muslims believe that Judas was made to take on the appearance of Christ and was crucified in his place as punishment for his treachery, and also deny that Christ is the Christ, the Messiah, which is obviously a problem, but their beliefs are close enough to Christianity so that the early church classified Islam as an heretical cult rather than a different religion such as Zoroastrianism, which, incidentally, has enough parallels with Judaism that one suspects Zoroaster may have been a failed prophet, for instance if Jonah had compromised his faith with that of the Ninevites) or teach that we can be saved on our own merit, we have the Nicene Creed in its Constantinopolitan format,
which ChristianForums provides on our forum’s statement of faith complete with Scripture citations. I shall post it here so you can study it - this is the primary Christian creed and has been since shortly after the Council of Constantinople concluded in 381 AD:
The Nicene Creed
We believe in (
Romans 10:8-10;
1John 4:15)
ONE God, (
Deuteronomy 6:4,
Ephesians 4:6)
the Father (
Matthew 6:9)
Almighty, (
Exodus 6:3)
Maker of Heaven and Earth, (
Genesis 1:1)
and of all things visible and invisible. (
Colossians 1:15-16)
And in ONE Lord Jesus Christ, (
Acts 11:17)
the Son of God, (Mathew 14:33; 16:16)
the Only-Begotten, (
John 1:18;
3:16)
Begotten of the Father before all ages. (
John 1:2)
Light of Light; (
Psalm 27:1;
John 8:12;
Matthew 17:2,
5)
True God of True God; (
John 17:1-5)
Begotten, not made; (
John 1:18)
of one essence with the Father (
John 10:30)
by whom all things were made; (
Hebrews 1:1-2)
Who for us men and for our salvation (
1Timothy 2:4-5)
came down from Heaven, (
John 6:33,
35)
and was incarnate of the Holy Spirit and the Virgin Mary, (
Luke 1:35)
and became man. (
John 1:14)
And was crucified for us (
Mark 15:25;
1Cointhians 15:3)
under Pontius Pilate, (
John 19:6)
and suffered, (
Mark 8:31)
and was buried. (
Luke 23:53;
1Corinthians 15:4)
And the third day He rose again, according to the Scriptures. (
Luke 24:1 1Corinthians 15:4)
And ascended into Heaven, (
Luke 24:51;
Acts 1:10)
and sits at the right hand of the Father. (
Mark 16:19;
Acts 7:55)
And He shall come again with glory (
Matthew 24:27)
to judge the living and the dead; (
Acts 10:42;
2Timothy 4:1)
whose Kingdom shall have no end. (
2 Peter 1:11)
And in the Holy Spirit, (
John 14:26)
the Lord, (
Acts 5:3-4)
the Giver of Life, (
Genesis 1:2)
Who proceeds from the Father; (
John 15:26)
Who with the Father and the Son together is worshipped and glorified; (
Matthew 3:16-17)
Who spoke through the prophets. (
1 Samuel 19:20 ;
Ezekiel 11:5,
13) In one, (
Matthew 16: 18)
holy, (
1 Peter 2:5,
9)
catholic*, (
Mark 16:15)
and apostolic Church. (
Acts 2:42;
Ephesians 2:19-22)
I acknowledge one baptism for the remission of sins**. (
Ephesians 4:5;
Acts 2:38)
I look for the resurrection of the dead, (
John 11:24;
1Corinthians 15:12-49;
Hebrews 6:2;
Revelation 20:5)
and the life of the world to come. (
Mark 10:29-30)
AMEN. (
Psalm 106:48)
Notes
* The word "catholic" (literally, "complete," "universal," or "according to the whole") refers to the universal church of the Lord Jesus Christ and not necessarily or exclusively to any particular visible denomination, institution, or doctrine.
** May be interpreted as baptism is a matter of obedience and not a requirement for salvation or as a regenerating ordinance.