The theology of Andrew Fuller, as set out in his greatest work, The Gospel Worthy of All Acceptation, is centrally located between those Calvinists who see sinners as walking corpses—no more able to believe than a dead body is able to raise itself from the dead—and those of the other side who see sinners as fully enabled by God’s grace to choose (their will being the determining factor). To Fuller, men are able to believe, but will nonetheless remain unwilling until God does a supernatural work of grace to reverse their unwillingness. Regeneration only causes a man to do what he otherwise could have and should have done but refused. This puts the feet of the universal gospel offer on much more Biblical ground, and removes much of the repugnance of the Calvinist doctrine. The gospel is to be preached to all men because all men do have the ability—and the warrant—to embrace it; and that gospel would save any who do—even the unelect if they would but be willing.
What then of inability? Fuller explains, “It is common, both in Scripture and in conversation, to speak of a person who is under the influence of an evil bias of heart, as unable to do that which is inconsistent with it.” As an example, Fuller offers Gen. 37:4, in which it is said that Joseph’s brothers “could not speak peaceably” to Joseph. It is universally understood that such an inability was not meant in the literal, natural sense of being absolutely unable—like a mute man being unable to speak anything, but only in the figurative, moral sense of being unable to find it within their hearts to speak peaceably to him. And it is just as universally understood that the former meaning provides an excuse while the latter does not.
That is Fuller’s view in a nutshell, when it comes to the inability of sinners to believe in Christ or do what is right: they cannot find the willingness in their heart, but the ability—in the natural sense of that word—remains just the same, so that they are left without excuse. They are unable to believe, in the moral sense of that word, just as Joseph’s brothers were unable to speak peaceably to him. This is what Fuller understands in the Bible’s descriptions of sinners as unable to come to Christ. And it fully resolves the seeming tension with the Bible’s description of sinners as unwilling to come to Christ, as well as the “Divine censure” that attends such an unwillingness.
To Fuller, one is excused only when one is absolutely unable, such as a physically blind man being excused from reading Scripture. This is inability in its natural sense, and presupposes an absoluteness that could not be overcome no matter how much the man might be willing. Therefore, a man who is not physically blind but refuses to see due to the wickedness of his heart is without excuse, since his inability to see is in the moral sense of the word, which presupposes that a natural ability remains by which he could see if he really wanted to. Natural inability presupposes an absolute inability; while moral inability presupposes a remaining natural ability.
Although Fuller saw the inability of sinners in this figurative, moral sense, such that sinners are naturally able to believe simply by choosing to do so, he was also committed to the Calvinist understanding that no man will believe apart from God’s supernatural work of grace. The unwillingness in men’s hearts will remain until God changes it. God offers salvation to all who hear the gospel, with a full warrant to believe and be saved; but sinners will refuse to exercise their natural ability to believe until persuaded through God’s work of grace. In each case, it is God alone who chooses whether to persuade a man and bring him to faith or leave him in his sinful aversion. And He uses the preaching of the gospel in that persuasion. “Therefore, we are ambassadors for Christ, certain that God is appealing through us. We plead on Christ’s behalf, ‘Be reconciled to God!'”
[For an in-depth engagement of these matters, see “Fuller & Inability: A Centrist Response to Tom Nettles.”]