John Gill Commentary Exodus 33:21

"and Jehovah said, Behold, there is a place by me, and thou shalt stand upon the rock:" — Exodus 33:21 (ASV)

And the Lord said, behold, [there is] a place by me
Near him, not in or by the tabernacle, where it may be the pillar of cloud now was, as it had been, (Exodus 33:9Exodus 33:10) but upon the rock, where it had been for many days, and near to which there was a fit place for Moses to be in, and have that view of the goodness and glory of God he would favour him with:

and you shall stand upon a rock ;
in Horeb, typical of Christ the rock, the rock of Israel, and the rock of ages, the rock of refuge, salvation, and strength; comparable to one for shelter, solidity, firmness, strength, and duration; and happy are they who stand upon this rock; they are safe and secure, they stand on high, and have noble prospects of the perfections of God, and of the riches of his grace and goodness, see (Psalms 50:2Psalms 50:3) (Isaiah 33:16Isaiah 33:17) (Matthew 7:24Matthew 7:25) .