He is shaking all that can be shaken so that what remains is that which cannot be shaken
Hebrews 12:26 His voice shook the earth at that time, but now he has promised, Yet once more I will shake not only the earth but also the heavens. 27 This expression, “Yet once more,” indicates the removal of what can be shaken—that is, created things—so that what is not shaken might remain. 28 Therefore, since we are receiving a kingdom that cannot be shaken, let us be thankful. By it, we may serve God acceptably, with reverence and awe.