Mutability and time go hand in hand. Sometimes the world changes suddenly, but more often it changes gradually, over time, so slowly that we don’t even notice. And sometimes the first kind of change leads to the second, as with the tower that gets knocked over by time’s erosion. Older things, of course, are more likely to fall prey to time. Wordsworth was middle-aged when he wrote "Mutability," so he probably had the effects of time on his mind. When we’re young we think of ourselves as indestructible, but Wordsworth’s metaphor of the falling tower shows how far this image is from reality.
Wordsworth embeds subtle allusions to the passing of time in the poem, such as the use of "low to high" and "high to low" to hint at the movement of the sun.
According to the poem, criminals and greedy and over-anxious people cannot understand change because they are too focused on short-term goals and problems; they cannot take a longer view.