When to Pray
"Truly, truly, I say to you, whatever you ask of the Father in My name, He will give it to you."
When to Pray
If you refuse to pray until you know or feel yourself worthy and fit, you need never pray any more. For as was said before, our prayer must not be based upon or depend upon our worthiness or that of our prayer, but on the unwavering truth of the divine promise. Whenever our prayer is founded on itself or something else, it is false and deceptive, even though it wrings your heart with its intense devotion or weeps sheer drops of blood (Luke 22:44). We pray after all because we are unworthy to pray. The very fact that we are unworthy and that we dare to pray confidently, trusting only in the faithfulness of God, makes us worthy to pray and to have our prayer answered. Be as unworthy as you may, but know most seriously that it is a thousand times more important, yes, that everything depends on your honoring God's truthfulness and your never giving His promise the lie by your doubts. Your worthiness does not help you; and your unworthiness does not hinder you. . .. All your life you must, therefore, guard against deeming yourself worthy or fit to pray or to receive, unless it be that you proceed with bold courage, trusting in the truthful and certain promises of your gracious God, who thereby wants to reveal His mercy to you.
From On Rogationtide Prayer and Procession (Luther's Works 42:88- 89)