Jamieson, Fausset and Brown on Hebrews 12:26

26. then shook--when He gave the law on Sinai.

now--under the Gospel.

promised--The announcement of His coming to break up the present order of things, is to the ungodly a terror, to the godly a promise, the fulfilment of which they look for with joyful hope.

Yet once more--Compare Notes, see on Hag 2:6; Hag 2:21, 22, both of which passages are condensed into one here. The shaking began at the first coming of Messiah; it will be completed at His second coming, prodigies in the world of nature accompanying the overthrow of all kingdoms that oppose Messiah. The Hebrew is literally, "it is yet one little," that is, a single brief space till the series of movements begins ending in the advent of Messiah. Not merely the earth, as at the establishment of the Sinaitic covenant, but heaven also is to be shaken. The two advents of Messiah are regarded as one, the complete shaking belonging to the second advent, of which the presage was given in the shakings at the first advent: the convulsions connected with the overthrow of Jerusalem shadowing forth those about to be at the overthrow of all the God-opposed kingdoms by the coming Messiah.