All the commentators agree that this verse establishes a direct cause-and-effect relationship. Sickness, suffering, and calamity are presented as consequences of sin. Therefore, the promise that 'the inhabitant shall not say, I am sick' is a direct result of the fact that 'the people that dwell therein shall be forgiven their iniquity.' As John Calvin explains, when the root cause (sin) is removed, the effect (suffering) is also removed.