DEVOTION//The Bible is truth
Martin Luther staunchly believed that the Bible is God's Word and absolute truth. He warns that, when people fail to rest their faith on that foundation, they soon deny the Christian faith. Let’s allow Luther to speak:
The basic principle of faith in Christ
We are addressing people who regard God as a true God, who is truthful and does not lie, people who regard the apostles as his ambassadors and witnesses, as men who proclaim his Word and who must be heard as he himself is heard. As Christ says (Luke 10:16): “‘He who hears you hears me,’ and he who hears me hears my Father.”
Those are our principia, the basis and the chief article on which the entire Christian doctrine is founded. For all of Scripture asserts solely of that God and of His Son and apostles that their proclamation constitutes the right Word of God and that whoever believes this will be saved.
To deny the Bible is God’s Word denies Christ
If you deny all of that, I shall have nothing to do with you. For whoever denies God and his Word, his Baptism and gospel, will not find it hard to deny the resurrection of the dead as well. If you dare to say that God is not God and that the apostles and Christendom do not teach and believe correctly, it is easy for you—and nothing seems better—to knock the whole bottom out of the barrel and say that there is no resurrection, neither heaven nor hell, neither devil nor death nor sin, etc. For what will you believe if you do not believe that God is something?
Faith in God’s Word is a mark of Christianity
But if you choose to be numbered among those who regard God and his apostles, his Word, and Christendom as truthful, we shall indeed convince and constrain you to believe also this article. For what Christendom believes and the apostles proclaim cannot be a lie.
Thus it is also impossible for the apostles to be false witnesses of God; otherwise God would not be truthful and could not be God.
Now that these principia stand, it follows logically and necessarily that you have to believe the resurrection of the dead, as surely as God is God. For he revealed the resurrection through his Son in Scripture and had it proclaimed through the apostles; and it was accepted and believed by Christendom. … It must be correct and true.
Source: Luther’s Works, Vol. 28, pp. 95–97: 1 Corinthians 7, 1 Corinthians 15, Lectures on 1 Timothy. Saint Louis: Concordia Publishing House.