By contrast, if God works in us, the will is changed, and being gently breathed upon by the Spirit of God, it again wills and acts from pure willingness and inclination and of its own accord, not from compulsion, so that it cannot be turned another way by any opposition, nor be overcome or compelled even by the gates of hell, but it goes on willing and delighting in and loving the good, just as before it willed and delighted in and loved evil. This again is proved by experience, which shows how invincible and steadfast holy men are, who when force is used to compel them to other things are thereby all the more spurred on to will the good, just as fire is fanned into flames rather than extinguished by the wind. So not even here is there any free choice, or freedom to turn oneself in another direction or will something different, so long as the Spirit and grace of God remain in a man.
In short, if we are under the god of this world, away from the work and Spirit of the true God, we are held captive to his will, as Paul says to Timothy [II Tim. 2:26], so that we cannot will anything but what he wills. For he is that strong man armed, who guards his own palace in such a way that those whom he possesses are in peace [Luke 11:21], so as to prevent them from stirring up any thought or feeling against him; otherwise, the kingdom of Satan being divided against itself would not stand [Luke 11:18], whereas Christ affirms that it does stand. And this we do readily and willingly, according to the nature of the will, which would not be a will if it were compelled; for compulsion is rather (so to say) “unwill.” But if a Stronger One comes who overcomes him and takes us as His spoil, then through his Spirit we are again slaves and captives—though this is royal freedom—so that we readily will and do what he wills. Thus the human will is placed between the two like a beast of burden. If God rides it, it wills and goes where God wills, as the psalm says: “I am become as a beast [before thee] and I am always with thee” [Ps. 73:22 f.]. If Satan rides it, it wills and goes where Satan wills; nor can it choose to run to either of the two riders or to seek him out, but the riders themselves contend for the possession and control of it.
The Bondage of the Will
Luther’s Works Vol. 33