Albert Barnes on Acts 7:33

Then said the Lord, etc. In Ex 3 this is introduced in a different order, as being spoken before God said, "I am the God," etc.

Put off thy shoes, etc. Ex 3:5. To put off the shoes, or sandals, was an act of reverence. Especially the ancients were not permitted to enter a temple or holy place with their shoes on. Indeed, it was customary for the Jews to remove their shoes whenever they entered any house, as a mere matter of civility. Comp. Jn 13:6. See Josh 5:15.

Is holy ground. Is rendered sacred by the symbol of the Divine Presence. We should enter the sanctuary, the place set apart for Divine worship, not only with reverence m our hearts, but with every external indication of veneration. Solemn awe, and deep seriousness, become the place set apart to the service of God.

(b) "Put off thy shoes" Josh 5:15, Eccl 5:1