"The cabinet of the mysterious Trinity": reserve and moderation in Trinitarian claims as a matter of revelation

And what can more ennoble our nature, than that by the means of his holy humanity it was taken up into the cabinet of the mysterious Trinity? - The Great Exemplar I.I.ad1 on the Annunciation and Conception of the Lord.

In the midst of two thieves, three long hours the holy Jesus hung clothed with pain, agony, and dishonour; all of them so eminent and vast, that he who could not but hope, whose soul was encased with divinity, and dwelt in the bosom of God, and in the cabinet of the mysterious Trinity - The Great Exemplar III.XX.9 on the Passion of the Lord.

In his meditations on the beginning and the ending of the Lord's earthly life, Taylor employs the phrase "the cabinet [i.e. the private inner room] of the mysterious Trinity".  It is suggestive of what is not revealed to humanity: the inner life of the Godhead is closed to us.  Similar wording is used in The Great Exemplar (III.XVI.2) when Taylor discusses God's "secret counsel" of predestination:

But his peremptory, final, unalterable decree, he keeps in the cabinets of the eternal ages, never to be unlocked till the angel of the covenant shall declare the unalterable universal sentence.

The cabinet - whether of the Holy Trinity or of predestination - is not open to humanity's gaze. 

Except, that is, for one event when the cabinet of the Trinity was, in a manner, opened before humanity:

this was the greatest meeting that ever was upon earth, where the whole cabinet of the mysterious Trinity was opened and shown, as much as the capacities of our present imperfections will permit; the second person in the veil of humanity; the third in the shape, or with the motion of a dove; but the first kept his primitive state: and as to the Israelites he gave notice, by way of caution, ' Ye saw no shape, but ye heard a voice'; now also God the Father gave testimony to his Holy Son, and appeared only in a voice, without any visible representment.

Notice the need for reserve and moderation even here: the cabinet is open "as much as the capacities of our present imperfections will permit"; the Second Person of the Blessed Trinity is revealed "in the veil" of incarnate humanity, the Third "in the shape" of the dove; the First Person is heard, not seen, in continuity with the revelation to Israel.  This one event when "the cabinet of the mysterious Trinity" is opened before humanity does not reveal the inner life of the Godhead.  

What is more, the cabinet is not opened again.  This is the only event which Taylor describes as an opening of the cabinet, the clearest and fullest revelation of the Holy Trinity.  Our confession of the Holy Trinity, then, should not exceed what is revealed at the theophany that is the Baptism of Our Lord (hence Taylor's view - more of much tomorrow - that the Apostles' Creed is the normative and authoritative statement of Trinitarian doctrine).  This emphasises the extent to which Taylor's insistence on moderation and reserve in Trinitarian claims flows from nothing akin to the rationalist scepticism of the Socinians but from the order of revelation itself and a reverence for what is revealed. 

That we need no more than this is also hinted at in Holy Living, when Taylor uses the same phrase to describe the mystery of our indwelling by the Trinity:

The temple itself is the heart of man; Christ is the high-priest, who from thence sends up the incense of prayers, and joins them to his own intercession, and presents all together to his Father; and the Holy Ghost, by his dwelling there, hath also consecrated it into a temple; and God dwells in our hearts by faith and Christ by his Spirit, and the Spirit by his purities: so that we are also cabinets of the mysterious Trinity; and what is this short of heaven itself, but as infancy is short of manhood, and letters of words? The same state of life it is, but not the same age. It is heaven in a looking-glass, dark, but yet true, representing the beauties of the soul, and the graces of God, and the images of his eternal glory, by the reality of a special presence.

To go beyond the bounds of revelation, to speculate about the inner life of the Blessed and mysterious Trinity, is to demonstrate an irreverent presumption, for we have been given "heaven in a looking-glass, dark, but yet true".