"Do you doubt whether God has heard you, because you are a sinner? then cling to the word and say: Though I am a sinner and unworthy, yet I have the command of God, that tells me to pray, and his promise that he will graciously hear me, not because of my worthiness, but for the sake of the Lord Christ…
Pray, not regarding your worthiness or unworthiness, but your need and his word upon which he tells you to build; especially since he has placed before you and put into your mouth the words how and what you are to pray for…so that you joyously send up these prayers through him, and can lay them in his bosom, that he may lay them by his own worthiness before the Father…
As a Father he has promised to hear and help us…pray with hearty confidence, and rely upon this prayer, as assuredly heard, and await help."
—Martin Luther, Commentary on the Sermon on the Mount