A Voice from the Past - Luther

Wherefore it ought to be the first concern of every Christian to lay aside all confidence in works and increasingly to strengthen faith alone and through faith to grow in the knowledge, not of works, but of Christ Jesus, who suffered and rose for him, as Peter teaches in the last chapter of his first Epistle (1 Peter 5:10).

Martin Luther, 1483-1546, The Freedom of a Christian, (Luther's Works, edited by Harold J. Grimm, Muhlenberg Press, 1957, Career of the Reformer: I, Vol. 31, p. 347)

What should Christians base their confidence on? Why is this important?