Truly, I believe that the greatest error in the doctrines and traditions of mortal men (which I personally eschew) is that they try to anthropomorphize God.
Only God knows objective Truth. A thing is true because He says it. And all we can confidently know of Him is what He reveals to us.
But mankind seems to want a small 'god' it can obtain, understand, meet eye-to-eye, tell what to do and wrestle with.
When we ultimately realize that being made in His image doesn't mean that God is like man, we are brought to our knees and that cavalier attitude about the Father, the Son and the Holy Spirit dies.
And he [was] clothed with a vesture dipped in blood: and his name is called The Word of God.
And the armies [which were] in heaven followed him upon white horses, clothed in fine linen, white and clean. And out of his mouth goeth a sharp sword, that with it he should smite the nations: and he shall rule them with a rod of iron: and he treadeth the winepress of the fierceness and wrath of Almighty God.
And he hath on [his] vesture and on his thigh a name written, KING OF KINGS, AND LORD OF LORDS. - Rev 19:11-16
Excellent post, A-G. I would add the following about objective Truth:
And those to whom He reveals Truth know the revealed Truth.
But, you are correct that the full range of objective Truth is known only to God.
Jesus said to Pilate: "I came to testify to the Truth."