I don't believe I know God.
The presence or absence of the semicolon in the above sentence changes the meaning of the statement; and it changes the meaning of each of the words in the statement. With the semicolon, it is a mystics statement; without, it is agnostic..
The "I" who knows God and the "I" who doesn't think he knows God are different "Is" The latter is the ego. I, who possess this mind, this intellect, this thought, I who have a certain investment in my agnosticism. If I believed in God, I would have the same kind of ego investment in that belief. Information challenging that belief would challenge me. The God known to the mystic is not known by the ego or the intellect. Intellectually, tje mystic does not have some factility for knowing God that other people lack. The mystic has trained his intellect, or been given the grace to suspend his intellect) so that it does not get in the way of God's making her/him/itself known to the soul and heart, which have become the mystic's "me."
"Don't" is a barrier for the agnostic; Thou shalt not believe in what has not been demonstrated empirically to be believeable. "Don't, for the mtstic, is a simple absense of "do." The knowledge, or whatever you want to call it, comes to me as a gift when I do not stand in my own way--when I do not stand in the way of that gift.
"Believe" and "know" also take on different meanings in the two sentences, and those different meanings should lead to different action and different qualities of belief and knowledge. The agnostic says: my opinion about the existence of God has so little evidence to support it that I would prefer to express no opinion at this time. The mystic says faith and trust are concepts too puny to deal with the sense of the divine that I have experienced. Both are saying they "don't believe" in God. One finds lack of belief to be a problem, the other has gone beyond the need for belief. This is because the knowleges involved are very different. Again, the agnostic's is intellectual, the mystic's is spiritual.
The meaning of "God" in the two statements is also very different. The agnostic's God is the same as the theist's God. This God has attributes sych as goodness, power, majesty, jealousy, kindness which can be acknowledged or denied by the ego. You say God is just, well how about this atrocity or that flaw in creation. The "God of Abraham, Isaac, and Jacob" who will converse, play cruel pranks, wrestle, and abet fraud.-- Neither agnostics nor mystics show much interest in this God. The god beyond all gods, Brahman (not Brahma), The Godhead (not exactly the Trinity), the Tao, The "pure light of the void" are meaningful nonsense, not to be spoken of except in ecstatic outburst, the result of unadulterated experience of that which is beyond experience.
Tje categories of agnostic and mystic rarely overlap. There may be a number of reasons for this, but I think they are mostly cultural.. Buddhism is hightly mystical and inclined toward agnosticism. The Tao te Ching is a great classic in mysticism and agnosticism. I was going somewhere with this, but the process seems to have stopped. Maybe more later.