Consider the famous line from "The Lady of Shalott,"
Four gray walls, and four gray towersWhat does the first "four" give us? With "walls" we have a image of imprisonment. The four right angles implied invokes rationalism: closed rather than open, and associated with controlling masculinity (cf. Gaskell's Cranford.) This masculine element of the enclosure is strengthened by the phallic "four....towers": alluding perhaps to four levels of men (incl. lover) The "four" additionally suggests enclosure for the four points of the compass (hat-tip classfellow J.F.). It is also a sharply non-religious number: odd additional from the scacred number three. It is also the number of iambs in the line. The second word, "gray," denotes colourlessness, which is a direct contrast with the vivid colour-words in the stanzas immediately surrounding (e.g. "blue," "yellow," "red.") Gray also has a moral connotation of being neither openly good (white) nor openly bad (black.) "Gray" is the colour of ambiguity, which sets up the quality of the Lady's ambiguous action in leaving the tower.
That certainly is the beginning of a close reading of this line (the structure of the parallel clauses has an intriguing relevancy.) It is just to give another illustration of the level of detail that a close reading has. And of course your own close reading will likely differ from this: in tutorial this week, a classfellow pointed out that l.485 of bk.2 of Aurora Leigh--'life develops from within'--adds a maternal dimension to the passage: a reading which, you won't be surprised to hear, had hitherto evaded me.