Earthly, material things (i.e., things that can be "shaken") will not last forever. By contrast, God's kingdom is unshakable, and the author uses the contrast as an exhortation to right conduct. He has made it plain that God will not trifle with wrongdoing. The persistent sinner can count on severe judgment. God will bring all things present to an end. Accordingly, the readers should serve him faithfully.
27 The writer picks out the expression 'once more" to point out the decisive significance of the things of which he is writing. There is an air of finality about it all. "The removing" of which can be shaken will occur in the final day. This physical creation can be shaken, and it is set in contrast to what cannot be shaken-the things that really matter. The author does not go into detail about the precise nature of the ultimate rest. "So that" introduces a clause of purpose. It is God's will for this final differentiation to be made so that only what cannot be shaken will remain.
28 The "kingdom" is not a frequent subject in this letter. This is in contrast to the Synoptic Gospels where 'Kingdom" frequently occurs in the teaching of Jesus. But this passage shows that the author understood ultimate reality in terms of God's sovereignty, in contrast with earthly systems. They can be shaken and in due course will be shaken. Not so God's kingdom! The author does not simply say that it will not be shaken but that it cannot be shaken. The kingdom is something we "receive." It is not earned or created by believers; it is God's gift (Luke 12:32).
[NIV BIBLE COMMENTARY Volume 2: New Testament].
JESUS IS LORD.