This is one of the crucial lines from Milton’s sonnet, ‘On His Blindness’. This is a concluding sentence, and the proverbial sentence of the poem means that God does not require any active service from his creatures. What he requires from man is obedience to his commandments. Those who only stand and wait at His service also serve Him, as do His trusted angels. It means those who surrender themselves to His will and act as per the wishes of the Almighty are also doing a service. The persons who, though not putting in any active service, are always at the call of Him are not lesser devotees.