Romans
Martin Luther ...
"I greatly longed to understand Paul's Epistle to the Romans, and nothing stood in the way but that one expression, 'the righteouness of God,' because I took it to mean that righteousness whereby God is righteous and deals righteously in punishing the unrighteous...

Night and day I pondered until... I grasped the truth that the righteousness of God is that righteousness whereby, through grace and sheer mercy, he justifies us by faith.

Thereupon I felt myself to be reborn and to have gone through open doors into paradise."