Regarding question 1

In the context of the English Revolution, I think that the line "They also serve who only stand and wait" could be interpreted as a passive call to action. Because this line does not use conventional syntax, many poets met the demand of their forms (meter, rhyme scheme, etc.) by using odd phrasing such as this, the line might more clearly read, They who only stand and wait also serve. While one might argue that the phrase is truncated, meaning that a word has been omitted to serve the same aforementioned purpose, this makes little sense because it would change the meaning of the phrase entirely. For example, if the omitted word was "those" (as in They also serve those who stand and wait) such an omission completely alters the reader's perception of the phrase. Therefore, it seems unlikely that Milton, or any poet, would have made such a change. So, let's go with the first interpretation of the line.

Here, Milton suggests that those who take no action still serve a purpose. If one is looking to this line for support of the English Revolution, one might argue that it means that anyone who did not take action against the English goverment was serving its purpose, but I think it would be wrong to make such a leap. The best reading of this line follows the tone of the rest of the poem, which is not political but spiritual. Milton expresses frustration that his blindess has rendered him incapable of serving God as well as he would like. However, Milton rationalizes, his blindness was given to him by God and concludes that "God doth not need / Either man's work or his own gifts" and that those who serve God best stand and wait for His instruction. This notion is what Milton expresses in the last line of the poem.