“The foundations of the thresholds shook.” The text does not tell us why this particular area was singled out and described. It is possible that the Seraphim were sort of doorkeepers, so the area where they were shook.

“house.” The Temple was the “house” of God, and was often just called “the house.”

“was filled with smoke.” The Temple in heaven was filled with smoke. Smoke is sometimes associated with the presence of God, as it is here. In Revelation 15:8 God was in His Temple in heaven surrounded by his “glory,” the brilliant and often multi-colored light that surrounded Him, and from His glory came smoke that filled the Temple. When God came down on Mount Sinai shortly after the Exodus from Egypt, the top of Mount Sinai was enveloped in smoke (Exod. 19:18).

[For more information on the glory of Yahweh, see commentary on Ezekiel 1:28.]