The sentence is part of a letter addressed to Coleridge that the poet cites in its entirety near the end of Chapter XIII of Biographia Literaria. In that chapter, Coleridge discusses his theory of the imagination; these thoughts were part of a longer essay that Coleridge planned to publish as the introduction to a volume of his poems.
The author of the letter has read the essay and describes the effect it had on his understandings and his feelings, and how readers of Coleridge's poems would receive the essay. For the anonymous author of the letter, the essay turned a number of ideas he held on their head. Then he goes on to provide arguments against publishing the essay as an introduction to a volume of poems.
- First, in spite of its length, some things had been left out, which made the content harder to understand.
- Second, readers would complain about it. Due to its length, the essay would significantly increase the price of the book into which Coleridge planned to include it. The content is also very abstruse and would better fit into a volume that is more theoretical by design.
At this point, the author adds, "I could add to these arguments one derived from pecuniary motives, ...". The phrase "the preceding" at the end of the sentence is short for "the preceding arguments", i.e. the arguments I summarised above.