But if we are unwilling to let this term go altogether—though that would be the safest and most God-fearing thing to do—let us at least teach men to use it honestly, so that free choice is allowed to man only with respect to what is beneath him and not what is above him. That is to say, a man should know that with regard to his faculties and possessions he has the right to use, to do, or to leave undone, according to his own free choice, though even this is controlled by the free choice of God alone, who acts in whatever way he pleases. On the other hand in relation to God, or in matters pertaining to salvation or damnation, a man has no free choice, but is a captive, subject and slave either of the will of God or the will of Satan.
The Bondage of the Will
Luther’s Works Vol. 33