In the first 57 lines, the speaker recounts how it has been five years since his last visit. He notes that during difficult times in his life, he has recalled the "beauteous forms" of the landscape of Tintern Abbey. These recollections have brought him "tranquil restoration."
Upon returning to this landscape five years later, he is comforted by the present experience but also looks forward to moments when he will look back again and use future recollections to regain a tranquil restoration.
While here I stand, not only with the sense
Of present pleasure, but with pleasing thoughts
That in this moment there is life and food
For future years.
It is just after these statements that the poet/speaker considers that while he hopes to have similar recollections in the future (as he did from his first visit five years ago), he realizes he has changed.
The speaker recalls that, five years ago, he came to the woods "more like a man / Flying from something that he dreads, than one / Who sought the thing he loved." As a younger man, he loved nature but experienced it in a more careless (or carefree) and passive way. His experience as a younger man was less profound; therefore, the beauty of nature "had no need of a remoter charm."
Around line 85, the speaker begins discussing the change. As an older man, he is less energetic physically (no longer bounding like a roe - deer), but he is a deeper thinker.
And I have felt
A presence that disturbs me with the joy
Of elevated thoughts; a sense sublime
Of something far more deeply interfused,
In the last section of the poem, Wordsworth hopes his sister ("my dearest Friend") will have a similar reaction to the natural landscape. He hopes that she will enjoy nature with carefree and joyous feelings. And when she grows older, he hopes she will have a deeper understanding, just as he did.
When these wild ecstasies shall be matured
Into a sober pleasure; when thy mind
Shall be a mansion for all lovely forms,
Thy memory be as a dwelling-place
For all sweet sounds and harmonies;