Charles Finney addresses the concepts of ability and inability in relation to obeying God's law, arguing that the distinctions made by various philosophers and theologians are nonsensical. He emphasizes that true moral ability exists within every individual, and that the Holy Spirit's role is to persuade rather than to make one able to obey. Finney asserts that God does not require the impossible from humanity, and that the real issue lies in the unwillingness to obey rather than an inability. He calls for a decisive commitment to serve God, echoing Joshua's challenge to the Israelites.