Adam Clarke on Isaiah 63:18

The people of thy holiness have possessed it but a little while "It is little that they have taken possession of thy holy mountain" - The difficulty of the construction in this place is acknowledged on all hands. Vitringa prefers that sense as the least exceptionable which our translation has expressed; in which however there seems to be a great defect; that is, the want of that in the speaker's view must have been the principal part of the proposition, the object of the verb, the land, or it, as our translators supply it, which surely ought to have been expressed, and not to have been left to be supplied by the reader. In a word, I believe there is some mistake in the text; and here the Septuagint help us out; they had in their copy הר har, mountain, instead of עם am, people, του ορους του ἁγιου σου, the mountain of thy Holy One. "Not only have our enemies taken possession of Mount Sion, and trodden down thy sanctuary; even far worse than this has befallen us; thou hast long since utterly cast us off, and dost not consider us as thy peculiar people." - L.