"They also serve who only stand and wait"-- Explain the line.

Answer : In Sonnet 19 written by John Milton, the poet laments for losing his eyesight without performing any worthy work when he had eyesight. He expresses his doubt if god will claim from him his due duties now. He knows that it is impossible for him to fulfill it if God demands so as he is blind. Then patients approaches and consoles the poet saying that the poet needs not to be worried. god is infinite and he has countless servants to perform restless duties all over the world. So God will not demand from the poet anything regarding his negligence. Patience assures the poet that they are also the real servant of God who have not done anything for god yet and just waiting to perform duties as soon as God will direct them like the men who always restlessly perform and obey God's order. Both type of men will get equal favour of God.