The Israelites were in bad shape in Isaiah 1. They were full of sin and alienated from God (Isaiah 59:1-2). Isaiah used the very striking metaphor of a sick man to describe their deplorable condition (vv. 5-6). Sin, the affliction of the heart, needs to be examined.
The malady of sin shows us that sin is loathsome in nature. God, who once beheld a man with delight, now beholds man full of sin and “pollution.” Sin easily spread from Eve all the way to the day when God regretted creating man (Genesis 6:6). Human reason, in all forms, has failed to restore a sinner back to God (cp. Ephesians 2:1-10).
The influence of sin affects the head, which is the seat of intelligence and knowledge, and the heart, which is the fountainhead of affection and love. When the mind is corrupt, it is impossible to restore the heart to health, for one cures the affliction by knowing goodness and truth (Philippians 4:8-9). Sin truly defiles us in so many ways.
The remedy of sin is scripture (Mark 7:21; Galatians 5:19). Be sure that you examine yourself and your condition before God. There is no way to do this without faithfully having knowledge of sin and its effects. Without the knowledge of sin, we can never come to true repentance of sin and will never seek our own salvation (Acts 2:38).
Even though Isaiah uses the striking example of the sick man, he also describes God’s willingness to offer salvation (vv. 18-20). Isaiah 33:24 states that no inhabitant of the land of Israel will be sick any longer. This is the wonderful effect of the gospel!