The "cannot be seen" vs "can be seen" is moral not optical question.
Ps 5:5 - The arrogant cannot stand in your presence. You hate all who
Rev 6:16-17 - Then the kings of the earth and the eminent people, and
the commanders and the wealthy and the strong, and every slave and
free person hid themselves in the caves and among the rocks of the
mountains; and they said to the mountains and the rocks, “Fall on us
and hide us from the sight of Him who sits on the throne, and from the
wrath of the Lamb; for the great day of Their wrath has come, and who
is able to stand?”
In fact, we also read that:
- John 1:18 - No one has ever seen God; the only God, who is at the Father’s side, he has made him known.
- John 6:46 - No one has seen the Father except the one who is from God; only he has seen the Father. (See also Matt 18:10.)
- 1 John 4:12 - No one has ever seen God; but if we love one another, God remains in us, and His love is perfected in us.
Thus, I conclude that OT epiphanies of YHWH were of Jesus and not the Father. In all these cases (eg, see appendix below) where people saw YHWH (the pre-incarnate Jesus) His full divinity was veiled so as not to endanger the lives of those who saw.
In the specific case of Ex 33 & 34, we read the specific request from Moses in Ex 33:18 as:
Then Moses said, “Please show me Your glory.”
This was a big ask and more than any sinful human could withstand and so God provided a compromise to only reveal part of the His glory - that of His back only and not of His face.
It is significant, that when the redeemed saints dwell in the New Jerusalem, their primary reward is to see the face of God and the Lamb, Rev 22:4.
APPENDIX - OT Epiphanies of YHWH
- Gen 18:1, 10 - Then the LORD appeared to Abraham by the Oaks of Mamre in the heat of the day, while he was sitting at the entrance of his tent. ... Then the LORD said, “I will surely return to you at this time next year, and your wife Sarah will have a son!”
- Gen 32:30 - So Jacob called the place Peniel, saying, "It is because I saw God face to face, and yet my life was spared."
- Ex 3:5, 6 - “Do not come any closer,” God said. “Take off your sandals, for the place where you are standing is holy ground.” Then He said, “I am the God of your father, the God of Abraham, the God of Isaac, and the God of Jacob.”
- Josh 5:13 - 6:2 - And the LORD said to Joshua, “Behold, I have delivered Jericho into your hand, along with its king and its mighty men of valor. (V2)
- Judges 6:14 - The LORD turned to him and said, “Go in the strength you have and save Israel from the hand of Midian. Am I not sending you?” [See also V16]
- Eze 1 - the prophet's vision of God; many elements of which are repeated in Rev 4 & 5.
- See also instances of the “Angel of the LORD” clearly being the LORD - Gen 16:7-13, 22:11-17, 32:24-30, 48:16, Ex 3:2-6, 32:34, Num 22:22-35, Josh 5:13-15, Judg 2:1-4, 6:11-23, 13:3-23, Isa 63:9, Dan 3:25, 28, Hos 12:4, 5, Zech 3:1-7, Mal 3:1, Rev 8:3-5, 10:1-10, 18:1, 20:1-4.
- A closely related phrase, “Angel of God” who is clearly God as in Gen 6:13, 8:15, 9:8, 17, 15:13, 17:3, 4, 21:12, 16-21, 35:1, 10, Ex 4:3-8, 6:2, 23:20, 21, Deut 1:6, 1 Kings 12:22, etc. See also Acts 10:3, 4, Gal 4:14.