Luther Defines the Gospel

In his 'Preface to the New Testament,' Luther writes:

This gospel of God or New Testament is
a good story and report,
sounded forth into all the world by the apostles,
telling of a true David
who strove with sin, death, and the devil,
and overcame them,
and thereby rescued all those who were
captive in sin,
afflicted with death,
and overpowered by the devil.

Without any merit of their own he
made them righteous,
gave them life,
and saved them,
so that they were given peace and brought back to God.

For this they sing,
and thank and praise God,
and are glad forever,
if only they believe firmly and remain steadfast in faith.

--Luther's Works 35:358