As a Calvinist, I believe in the doctrine of total inability, meaning that, apart from God's grace, sinful human beings are completely unable to repent and believe the gospel.
However, many object to this doctrine, believing that this sort of inability gives one an excuse for rejecting God's gracious offer of salvation. "How," it is asked, "can God hold men accountable for what they are unable to do?"
This objection is based on a confusion between two kinds of inability: natural and moral.
Natural inability is like my inability to outrun a speeding bullet or leap tall buildings. No one can rightly expect me to do those things because I'm simply not physically capable of doing them. This is natural inability.
A moral inability, though, is a very different kind of inability. Allow me to illustrate. Imagine a criminal pleading with a judge for leniency. He says, "Please, your honor, go easy on me. Yes, I committed this crime, but I only did it because I wanted to, and I enjoyed it." Does anyone seriously believe that this means the criminal is no longer culpable for his actions? This is moral inability. This is the kind of inability the Calvinist ascribes to unregenerate men.
When we say that fallen sinners, apart from God's grace, are unable to turn from their sin and trust Christ, we simply mean that they love evil and hate good so much that they will never (apart from the effectual calling of God) submit to Christ as Lord (Romans 8:7-8; cf. Romans 3:10-18; Jeremiah 17:9; Ephesians 2:1-3; 4:17-19; Psalm 14:2-3; Hebrews 11:6).
We are unable because we are unwilling. We can not because we will not. Nothing is stopping us except our twisted, sinful desires. Nothing is stopping us except our darkened hearts, and that is exactly what God changes in order to save us—our hearts. Total inability, as a consequence of original sin and a subset of total depravity, is a condition that we are
all born with this side of Eden, and it is a condition that can only be
overcome by being born again. This new birth is a mysterious act of God's irresistible, overcoming grace. Grace that overcomes our inability. Grace that creates ability. Grace that causes faith and repentance (John 3:3-8; cf. 1 Peter 1:3; Romans 4:17; Ephesians 2:8; Acts 11:18).