Concerning whom we have much to say, and hard to be interpreted in speaking of it, since ye are become dull in hearing.

to whom also a tenth of all did Abraham divide, (first, indeed, being interpreted, 'King of righteousness,' and then also, King of Salem, which is, King of Peace,)

Now the words, "once more" indicate the removing of what can be shaken --- that is, the created universe --- so that those things which cannot be shaken will remain. [Note: These "things" have been variously interpreted to be eternal truth, the heavenly kingdom, the new heavens and earth, etc.].