During the first 50 years of the Church, they did not have to address the attempts by various people to insert neo-platonist concepts into the teaching of Christ and the apostles resulting in the heresies of Arius or Nestorius and the rest. The creed was composed as a direct response to the heresy that the Logos was less than the Father (an "emination") and that the Holy Spirit was not a hypostasis of the trinity but merely the power of God.
But as to "not finding that emphasis in the NT", please consider:
I believe in God,(1) the Father Almighty,
Isaiah 44:6;
45:5
Maker of Heaven and Earth,(2)
Genesis 1:1;
John 1:1-3;
Acts 14:15
And in Jesus Christ,(3)
Luke 2:11;
John 20:28
His only begotten Son,(4)
John 3:16;
Proverbs 30:4
our Lord, (5)
John 20:28
begotten, not made
John 1:14,18; 3:16,18; 1JN 4:9
of one substance with the Father
Col 2:9
who was conceived by the Holy Spirit,(6)
Luke 1:35
born of the
Virgin(7) Mary,
Luke 1:27
suffered under Pontius Pilate,(8)
Luke 23:23-25
was
crucified,(9)
John 19:20;
Acts 4:10; all Gospels
dead(10)
1 Corinthians 15:3
and
buried.(11)
1 Corinthians 15:4
He descended into Hell.(A)
1 Peter 3:18;
Luke 23:43
The third day(12)
1 Corinthians 15:4
He arose from the dead,(13)
1 Corinthians 15:4
He ascended into Heaven(14)
Mark 16:19;
Luke 24:51,
Acts 1:11
and is seated at the right hand
of God,(15) the Father Almighty.
Mark 16:19;
Hebrews 1:3
From thence He shall come
to judge the living and the dead.(16)
2 Timothy 4:1;
John 5:22 ;
Mat 25
I believe in the Holy Spirit,(17)
John 15:26;
16:7-8, 13-14;
Acts 13:2
the church universal,(18)
Galatians 3:26-29
The apostolic church
Act 2:42;
2Th 2:15;
2Ti 2:2
the communion of saints,(19)
Revelation 19:14;
Hebrews 10:25
the forgiveness of sins,(20)
Luke 7:48
the resurrection of the body,(21)
1 Thessalonians 4:16;
John 6:39
and life everlasting.(22)
John 10:28;
17:2-3
I see no essential difference between those who were claiming to be of Cephas or of Apollos or of Paul and those declaring themselves to be Baptists or Methodists or Anglican of Pentecostal or whatever. By doing so, born again believers divide the the body of Christ and are in direct conflict with Jesus prayer in which He asked that we, the entire body of Christ" be one as He and the Father are one.
When Pentecostals say that Baptist churches are "dead" because they don't "have the Spirit" and when Baptists say that Pentecostals "have a demon" because they speak in tongues then they are very much indeed dividing the body of Christ as do multiple denominations who don't agree with each other all hold the opinion that the Roman Catholic Church is apostate and will have nothing to do with them, then they certainly do divide the body of Christ.
The is dividing started early with the "party of the Pharisees" who wanted the Gentile believers to be circumcised and to keep the Law of Moses. Paul called the dogs and preachers of "another Gospel" who were anathema.
Nothing has changed. The devil is still doing everything he can do to divide the body of Christ against itself so as to make it ineffective. The result can be seen in Europe and the USA being in a post-Christian decline into paganism and materialism (atheist socialism.)
If you can't see that then I can't show it to you.
iakov the fool