The sons' ultimate actions reveal their difference. The first son, after open refusal, repents of his sin—better late than never—and goes to work for his father. He overcomes and changes from bad to good. After experiencing the negative results of sin, he yields to God's instruction, changing direction and doing as his father commanded him—the fruit of his repentance.
The proof of our repentance comes to light when we comply with the Father's will and do good works with the help of the Holy Spirit. The result is the production of the fruit of the Spirit.