The OT is not functionally unitarian
Christian revelation cannot be functionally unitarian
God simply is trinity
Functional unitarianism can in no sense be a preparation for trinitarianism
The oneness of the triune God is nothing like the oneness of the unitarian god.
Trinity is not a nuance
There is no way to shove 'Trinity' in a corner while we discuss 'God'
Whatever 'God' we discuss at that point ceases to be the living God.
Jesus is not the cherry on top - He's the Rock, the Foundation
Jesus cannot be fitted into a pre-existing system but must from the outset define all things.
Jesus is not the Seal of a series of improving revelations - He is THE Word.
There is no concept of mediation which Jesus then fulfils. There is only The Mediator who mediates.
Mediation is by definition two-way. If the Mediator of knowledge is Himself unknown, mediation is not happening.
Knowing Jesus is essential.
'Progress towards Jesus' is not the unifying concept of the bible
Jesus Himself is the unifying Person of the bible.
Strictly the Person of Jesus is the object of saving faith, not the promises. Christ always comes clothed in the promises, but trust in the clothes doesn't save.
That'll do for now...