Free-will is plainly a divine term, and can be applicable to none but the divine Majesty only: for He alone “doth, (as the Psalm sings) what He will in Heaven and earth.” (Ps. cxxxv. 6.) Whereas, if it be ascribed unto men, it is not more properly ascribed, than the divinity of God Himself would be ascribed unto them: which would be the greatest of all sacrilege. Wherefore, it becomes Theologians to refrain from the use of this term altogether, whenever they wish to speak of human ability, and to leave it to be applied to God only. And moreover, to take this same term out of the mouths and speech of men; and thus to assert, as it were, for their God, that which belongs to His own sacred and holy Name. But if they must, whether or no, give some power to men, let them teach, that it is to be called by some other term than “Free-will”; especially since we know and clearly see, that the people are miserably deceived and seduced by that term, taking and understanding it to signify something far different from that which Theologians mean and understand by it, in their discussions. For the term, “Free-will,” is by far too grand, copious, and full: by which, the people imagine is signified (as the force and nature of the term requires) that power, which can freely turn itself as it will, and such a power as is under the influence of, and subject to no one. Whereas, if they knew that it was quite otherwise, and that by that term scarcely the least spark or degree of power was signified, and that, utterly ineffective of itself, being the servant and bond-slave of the devil, it would not be at all surprising if they should stone us as mockers and deceivers, who said one thing and meant something quite different; nay, who left it uncertain and unintelligible what we meant. For “he who speaks sophistically (the wise man saith) is hated,” and especially if he does so in things pertaining to godliness, where eternal salvation is at stake.
Martin Luther, Bondage of the Will, Sect. XXVI