Context : Milton became blind before half of his age. So he was very grieved. He thinks that the gift of poetry given by God is lying useless with him. He makes a protest against God. But soon he realizes his mistake. He comes to know that unconditional surrender to the will of God is the best service to Him.
Explanation : In this concluding stanza the poet says that the position of God is like kings. Thousands of angels are running continuously over land and ocean. They do not take rest and travel from one place to another. They convey the message of God to the poeple everywhere at His order. The sufferings and misfortunes of life are given to us by God as a test. So the best service to God is to bear these sufferings without any complaint.