I not only believe in Christ, but I know that He is sitting at the right hand of the Father to be our Mediator and to intercede for us. I know that the bread and the wine in the Lord’s Supper are the body and blood of Christ and that the word of the pastor, whether he preaches or absolves, is the Word of God. Yet the flesh is weighed down by doubt, so that it does not believe these things. This is great wretchedness and is bitterer than death itself. Indeed, the reason why death is bitter is that the hindrances of the flesh prevent us from believing. Otherwise affliction would be a joy, and death would be a sleep for us who believe.
We should deplore these evils, which are implanted in us through Adam as a result of original sin, and we should pray God to increase and strengthen faith in us and to sustain us under the heaven of the forgiveness of sins...
Luther’s Works, AE 5:21,
Lectures on Genesis,