Pr Eric Brown discusses Dr Martin Luther's comfort on prayer:

There is much angst, especially out here in the Bible Belt, over prayer. Prayer becomes a giant show, a harsh work, something that is difficult or embarassing. We need to "pray hard" - we need to be dilligent. Our prayers should be "ex corde" - from the heart, so if someone else writes them, they are no good.

And being hit by this, the Christian shrinks away, thinks how pitiful his ability to pray is, and is then put silent.

Contrast this with Luther - who yes, urges us to a diligent life and routine of prayer (remember your daily prayers from the catechism). But prayer is not difficult, it is not a show - even your constant prayer is not a burden. Why? Quoth Luther:

Wherever a Christian is, there the Holy Spirit is, Who does nothing else but pray constantly. For though a Christian is not moving his lips and speaking words, his heart nevertheless moves and beats (just like the pulse in his body) and always throbs with such sighs as these: Dear Father, may Thy name be hallowed; may Thy kingdom come; may Thy will be done by us and everyone. And the harder the blows of life or temptation and trouble press and beat upon him, the strong such sighs and prayers become, even vocally. Therefore you cannot find a Christian without prayer, just as you cannot find a living man without a pulse. The pulse never stands still; it is always throbbing and beating by itself, even though a man is sleeping or doing something else and, therefore, is not aware of it. (What Luther Says - 3487)

I love Luther. Whenever man goes and frets about what he is doing, if it is good enough, Luther like a thunderbolt flashes across the sky - it is about what God does! My prayer... not about me. It is the Holy Spirit at work in me, and while I might fail, He fails me never. My works... not about me - It is Christ who lives within me.

Luther is a man of comfort - he is a man of the Gospel.