The nature that Wordsworth knew as is the same nature which he knows now. The rainbow and the rose and the moon are all still there. Yet "The things which I have seen I now can see no more." Wordsworth can't see things quite the same as he once did; as a child, everything was a source of wonder, "Apparelled in celestial light." But now something seems missing to him. Wordsworth longs to be able to see things as he once did. But he acknowledges that he will never again be able to see things in the same way as a child.
However, by the end of the poem, Wordsworth comes to terms with this. He accepts that he can no longer see things as a child does. But he realizes that all hope is not lost. He still has his memories, and he has also gained wisdom in his years. He does not see things the same, but he appreciates them no less. Wordsworth has lost the ability to perceive things as a child, but he now has a different lens to view things through, the lense of wisdom and experience.