Then Luther makes an important distinction in explaining what he means by 'of necessity.' Very helpful, and strikingly similar to Edwards' Freedom of the Will.
Now, by 'necessarily' I do not mean 'compulsorily'. . . . That is to say, when a man is without the Spirit of God he does not do evil against his will, as if he were taken by the scruff of the neck and forced to it, like a thief or robber carried off against his will to punishment, but he does it of his own accord and with a ready will. And this readiness or will to act he cannot by his own powers omit, restrain, or change, but he keeps on willing and being ready; and even if he is compelled by external force to do something different, yet the will within him remains averse and he is resentful at whatever compels or resists it.--Bondage of the Will, in LW 33:64-65
He would not be resentful, however, if the will were changed and he willingly submitted to the compulsion. . . .
Ask experience how impossible it is to persuade people who have set their heart on anything. If they yield, they yield to force or to the greater attraction of something else; they never yield freely. . . .
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.
Sovereign, regenerating grace does not force us to do what we don't want to do. More deeply, it brings us to want to do what we should want to do. It gets underneath even our felt levels of desire.
I can get my 3-year-old Nathan into bed by picking him up, kicking and screaming, and carrying him. Or I can get him into bed by promising him that Where's Waldo and castle legos await him in his bed. Strategy #1 is not what Calvinists mean by irresistible grace.
But even strategy #2 doesn't quite capture it. Even in #2 Nate isn't getting into bed out of a delight to obey but because I've dangled something else in front of him. His desire to look for Waldo and play legos passes the threshold of his desire to stay downstairs. But he still doesn't delight in obedience. The will remains untouched. It is a book, not me, that he wants.
Irresistible grace is grace that softens us way down deep at the core of who we are. Taste bud transformation. In a miracle that can never be humanly manufactured, we find ourselves, strangely, delighting to love God.
This is a big God, with big grace.