To what does "this" refer in the opening of Wordsworth The Prelude?

It's been a little while since I read The Prelude. However, as I recall, The Prelude is more or less a poetic autobiography. And I believe that the "this" in these lines actually refers specifically to the poem itself. Wordsworth is questioning was it for "this" (specifically the poem, but more generally Wordsworth's poetic ability as exemplified by The Prelude) that I was exposed to these things or that these things happened/existed.