In the first volume of his Theological Studies, Baptist pastor Peter Ruckman writes:
Peter Ruckman - Theological Studies, Volume 1, Chapter 3
It must be emphasized that the Trinity still remains a mystery, basically, and that no single illustration can possibly explain everything about the Trinity. For example, you can't explain Christ saying "my Father is greater than I," when they actually have the same essence. You can only explain that in view of the fact that when Christ makes that statement He is on the earth in human form and the Father is not. You cannot fully explain the collapse of the Trinity into a Unity in eternity after Revelation 22 when the Son will "deliver up the Kingdom unto the Father" and then He Himself will submerge into God the Father so that God may be all in all the way it was before Genesis 1:1. However, we can use some illustrations to throw some light on the difficult and complex problem of the Trinity.
The most important thing we know about the Trinity is that it exists. It is not a Roman doctrine. It is a Bible doctrine. It is not the doctrine of Pastor Russell and Judge Rutherford. We firmly believe - any Christian firmly believes - that there is one God eternally existing and manifesting Himself to us in three persons: the Father, the Son, and the Holy Spirit.
Above, Peter Ruckman states that there will be a "collapse of the Trinity into a Unity in eternity after Revelation 22", where Jesus "will submerge into God the Father so that God may be all in all the way it was before Genesis 1:1", apparently referencing 1 Corinthians 15:28, which states:
1 Corinthians 15:27-28
27 For he hath put all things under his feet. But when he saith all things are put under him, it is manifest that he is excepted, which did put all things under him.
28 And when all things shall be subdued unto him, then shall the Son also himself be subject unto him that put all things under him, that God may be all in all.
This passage, from a Trinitarian perspective, is difficult, and typically requires a bit of explaining. However, there is no suggestion that Jesus will "submerge into God the Father", as Ruckman had stated. And, from the perspective of typical orthodox Trinitarian thought, such a statement would be strongly condemned in the harshest terms as, at the very least, very confusing, and if it means what it appears to mean - that Jesus will somehow ontologically change in the future - it would be condemned as "heresy" by virtually every Trinitarian.
He appears to teach something similar in his commentary on 1-2 Corinthians, namely, that Jesus will lose His "human nature" at some point in the future - a sort of undoing of the Hypostatic Union:
Peter Ruckman - 1-2 Corinthians Commentary, 15:28
So what it looks like from these verses is before Eternity begins Jesus Christ, the man, ceases to exist, and He goes back into the Godhead in His position as the Word of God (John 1:1-2). So God, as the eternal Trinity, is all there is; He is no longer "manifested in the flesh." I know that is hard to comprehend, but when has the Trinity ever been easy to understand?
So, why highlight these passages from Peter Ruckman's writings? Simply to demonstrate that so long as someone professes to be "Trinitarian", then they can hold to wildly divergent views of the doctrine, yet remain broadly accepted. Peter Ruckman was condemned by his contemporaries for many things during his life, but his view of the Trinity does not seem to be one of those things. However, consider if he had come out as a Unitarian. He likely would have been pilloried by even his most zealous supporters.
Yet, although he maintained what appears to have been a very strange, heterodox view of the Hypostatic Union from a Trinitarian point of view, because he professed to be a "Trinitarian", he avoided such scrutiny. He even drew a circle around Trinitarians when defining Christianity - "We firmly believe - any Christian firmly believes - that there is one God eternally existing and manifesting Himself to us in three persons" - despite he himself apparently holding a view that would be rejected by basically all Trinitarians in history as heretical.
Trinitarianism is, when closely analyzed, very fractured, with many distinct theories attempting to explain the doctrine, many of which are mutually exclusive. Yet, so long as one professes to be "Trinitarian", they will be able to remain within the "circle of orthodoxy" in the minds of very many Trinitarians, even if their views are very strange, or incongruent with another's proposed explanation of the Trinity.