"Seek the LORD while he may be found; call upon him while he is near; let the wicked forsake his way, and the unrighteous man his thoughts; let him return to the LORD, that he may have compassion on him, and to our God, for he will abundantly pardon."
The appealing motivation behind repentance is the compassionate forgiveness and love of God. This call to repentance is the result of the intense preaching of the prophet Isaiah brought to a personal passionate point. God loves to redeem fallen people. Any who seek Him will find Him ready to forgive and very near to them. From the human perspective, it must take a heart willing to forsake wicked ways, but when a sinner does so he finds a compassionate loving God ready to meet him at his knees.
It amazes me that God would reveal this kind of love for us. I want to be outraged over sin. I have no desire to restore a repentant person. Sin should be punished. Sinners deserve their misery. And that is why God is good and I am not. I deserve to be called to repentance for my own vindictive sense of sinful justice.
Thankfully, a holy God loves His creation. And He loves humanity. That love led Jesus to take on a body, live out the truth, and die to save us from our sin and all its consequences. It was that great love that Isaiah somehow saw in God. And it is that pardoning mercy that falls upon me in Jesus.