Charles Ellicott Commentary Isaiah 6:4

"And the foundations of the thresholds shook at the voice of him that cried, and the house was filled with smoke." — Isaiah 6:4 (ASV)

The posts of the door. —Better, the foundations of the threshold. The words seem to point to the prophet’s position as in front of the Holy of holies.

The house was filled with smoke. —The vision had its prototype in the smoke as of a furnace on Sinai (Exodus 19:18), in the glory-cloud of 1 Kings 8:10, and possibly in its lurid fire-lit darkness represented the wrath of Jehovah, as the clear brightness of the throne did His love. So in Revelation 15:8, the smoke from the glory of God precedes the outpouring of the seven vials of wrath.

The parallelism of the clouds of incense-smoke as the symbol of adoring prayer (Revelation 5:8; Revelation 8:4) suggests an alternative interpretation as possible; but in that case, mention would probably have been made of the censers from which it rose. The incense-clouds of the Temple may, in either case, have been the starting-point of the mystic vision.