Jesaja 6:4

When Isaiah heard this, he stood entranced at the farthest possible distance from Him that sat upon the throne, namely, under the door of the heavenly palace or temple. What he still further felt and saw, he proceeds to relate in Isa 6:4 : "And the foundations of the thresholds shook with the voice of them that cried; and the house became full of smoke." By ‛ammoth hassippim, the lxx, Vulgate, Syriac, and others understand the posts of the lintels, the supporting beams of the superliminaria, which closed the doorway at the top. But as saph is only used in other places to signify the threshold and porch (limen and vestibulum), ‛ammoth hassippim must be understood here in the (perfectly appropriate) sense of "the foundations of the thresholds" (ammâh, which bears the same relation to עם, mother, as matrix to mater, is used to denote the receptive basis into which the door-steps with their plugs were inserted, like the talmudic ammetâh derēchayyâh, the frame or box of the hand-mill (Berachoth 18b), and ammath megērah, the wood-work which runs along the back of the saw and keeps it firmly extended (Kelim 21, 3); compare the "Schraubenmutter," literally screw-mother, or female screw, which receives and holds the cylindrical screw). Every time that the choir of seraphim (הקּורא: compare such collective singulars as hâ'oreb, the ambush, in Jos 8:19; hechâlutz, of men of war, in Jos 6:7, etc.) began their song, the support of the threshold of the porch in which Isaiah was standing trembled. The building was seized with reverential awe throughout its whole extent, and in its deepest foundations: for in the blessed state beyond, nothing stands immoveable or unsusceptible in relation to the spirits there; but all things form, as it were, the accidentia of their free persona…

Hitherto, it should seem, Isaiah had prophesied as a candidate, having only a virtual and tacit commission; but here we have him (if I may so speak) solemnly ordained and set apart to the prophetic office by a more express or explicit commission, as his work grew more upon his hands: or perhaps, having seen little success of his ministry, he began to think of giving it up; and therefore God saw fit to renew his commission here in this chapter, in such a manner as might excite and encourage his zeal and industry in the execution of it, though he seemed to labour in vain. In this chapter we have, I. A very awful vision which Isaiah saw of the glory of God (Isa 6:1-4), the terror it put him into (Isa 6:5), and the relief given him against that terror by an assurance of the pardon of his sins (Isa 6:6, Isa 6:7). II. A very awful commission which Isaiah received to go as a prophet, in God's name (v. 8), by his preaching to harden the impenitent in sin and ripen them for ruin (v. 9-12) yet with a reservation of mercy for a remnant, (v. 13). And it was as to an evangelical prophet that these things were shown him and said to him.