Let's look at it:
We believe in one God,
the Father almighty,
maker of heaven and earth,
of all things visible and invisible.
And in one Lord Jesus Christ,
the only Son of God,
begotten from the Father before all ages,
God from God,
Light from Light,
true God from true God,
begotten, not made;
of the same essence as the Father.
Through him all things were made.
For us and for our salvation
he came down from heaven;
he became incarnate by the Holy Spirit and the virgin Mary,
and was made human.
He was crucified for us under Pontius Pilate;
he suffered and was buried.
The third day he rose again, according to the Scriptures.
He ascended to heaven
and is seated at the right hand of the Father.
He will come again with glory
to judge the living and the dead.
His kingdom will never end.
And we believe in the Holy Spirit,
the Lord, the giver of life.
He proceeds from the Father and the Son,
and with the Father and the Son is worshiped and glorified.
He spoke through the prophets.
We believe in one holy catholic and apostolic church.
We affirm one baptism for the forgiveness of sins.
We look forward to the resurrection of the dead,
and to life in the world to come. Amen
The context was over a dispute over the nature of the Deity. Arianism claimed a mystical, non human Jesus, or a created, non-divine advent. Modalism claimed different "modes' that God appeared through.
Athanasius, Irenaeus, and many other early apologists resisted the redefinings of the Apostle's teachings, and affirmed Jesus as 'very God of very God', and also fully man. They disputed both the mystisizing and any attempt to demean His Deity.
The term 'trinity', was not from Jesus nor the apostles, but was coined later, to describe the Triune God that Jesus described. The Father, the Son, and the Holy Spirit ALL are described and defined as God, by Jesus. I will take Him at His Word, lacking a more Authoritative source.