The term "eternal" Son is an extra Biblical term like the term Trinity. But not all Trinitarians agree that the Son was always the Son. Such as Dr. Walter Martin author of the Kingdom of the cults held the concept as not Biblcial. While it is true the Son is arguably called the Son prior to His incarnation, Isaiah 9:6, Proverbs 30:4, Psalms 2:12, the view of some Chrstians is the preincarnate Word did not become the Son of God until His incarnation, Luke 1:35.
Now I Believe the Word was the eternal Son based on the truth that He as "the unique Son" who appeard as God in the OT according to John 1:18. But if that reading is false and is really "the unique" or "unique, God" then I loose that proof text.
What proof text do you have for the concept of the "eternal Son?"
Some Christians believe that an essential doctrine must be clustered together in one place in the bible with every i dotted and t crossed'
This is not so. You mentioned the Trinity.
The word Trinity itself is not found in the bible, it took 3 centuries for the concept of the Trinity to be developed from the scriptures as opposed to Arianism (JWs are Arian).
Even after the efforts of Athanasius and the Council of Nicaea the church was and is still split over the matter.
Much, perhaps even most, of Christendom (even major denominations) is NOT Trinitarian but Arian.
While they claim to be Trinitarian they are actually Arian because they are modalists - Arian disguised as Trinitarian.
Such also the question of the eternal sonship of Christ has not been resolved by the church at large.
I believe the Logos to be the eternal Son of God who was/is the incarnation Jesus Christ.
The only begotten Son of God.
In Matthew 1 we see the word "begat" speaking of the human line leading to Joseph.
Jesus was not begotten of Joseph but of God the Father.
In fact He was the only Son begotten of God the Father.
You and I are born of the Spirit.
Why do I believe He is the eternal Son of God?
Because He emanates from the "bosom" of the Father. The innermost being of the Father.
bosom -
kolpos: 03788 the region of the body extending from the breasts to the legs, - Louw-Nida Lexicon
bosom -
kolpos:
23019-2 the womb - Liddell Scott Lexicon
They share the same essence of being.
And Jesus is THE ONLY ONE begotten of the Father in this manner.
Now is it an eternal relationship or not?
The scripture does not say in so many words whether it is eternal or not.
There are scriptures that can be used for eternal or temporal depending upon your choice of interpretation.
For almost 300 years Christendom floundered back and forth until Athanasius defined the Trinity and it was codified by the Council of Nicaea.
Ultimately your choice will determine if your are Trinitarian or Arian.
My choice - Jesus is the eternal son of God, the Second Person of the Holy Trinity.