What Faith Is
Wait for the LORD; be strong, and let your heart take courage.
What Faith Is
Faith is an all-powerful battle which, in opposition to the battle of the flesh, clings to the Word and the promise with one and the same prospect. . .. [David] felt much more unbelief than faith, for faith seems and is weak, because the flesh not only wages war but even takes captive, as Paul says in Romans 7:14. Formerly I had no other conviction than that Paul gave no thought at all to exerting himself and battling against the flesh. But he says (2 Corinthians 12:7): "A thorn was given me in the flesh, a messenger of Satan, to harass me." He teaches me what faith is. I see the glorious victories of the saints and the martyrs. But my faith cannot accomplish this. And they also exerted themselves and overcame death. They did not do this without a great conflict. Thus we, too, have the same Baptism, the same God to give consolation, and the Holy Spirit, the Comforter who offers us rich comfort in the Word. And although I gladly hear the account of the conflicts and the victories of the saints, I cannot do the same things. Therefore one must take hold of the Word (Psalm 27:14): "Wait for the Lord; be strong, and let your heart take courage." God does not abandon even him who is weak in faith.
From Lectures on Genesis (Luther's Works 5:131)