I will get you started on this and you can do the rest.
As you know, Milton lost his sight and in this sonnet, he is lamenting its loss yet trying to console himself that his life still has purpose. Milton had a deep knowledge of Scripture (that is how he was able to write Paradise Lost), and in this poem, you can see the influence of his faith. While he is exploring his feelings about being blind, he seeks comfort through his faith. There is a lot of light/dark imagery:
“my light is spent”
“ere half my days in this dark world and wide”.
He states that he still has gifts and “talents” and that he can use them to serve “my Maker.” He admits that God does not need his or anyone’s help:
God doth not need either man’s work or his own gifts
Nevertheless, God wants man to serve him. This Milton will do, and he says that he will wait on God to let him know the direction this service will take him, even though he may not be able to use his former gift of writing to serve God. When God closes one door, he opens the other. This is what Milton believes.
Look at the structure of the poem and see how he uses language to express this idea. There are lots of poetic devices and the word choices evoke a quiet, contemplative mood. Read more about Milton here on enotes.