"For as the heavens are high above the earth, So great is His mercy toward those who fear Him;" Psalms 103:11

The fundamental truth of this verse is this: The distance that separates the Heavens from the earth is boundless, and so is God's mercy. 
The concept of comparing the Heavens high above the earth, and the character of God is not foreign to the Scriptures. 

"Let the wicked forsake his way, And the unrighteous man his thoughts; Let him return to the Lord, And He will have mercy on him; And to our God, For He will abundantly pardon." Isaiah 55:7
Why will He "abundantly pardon?"
"For My thoughts are not your thoughts, Nor are your ways My ways," says the Lord. For as the heavens are higher than the earth, So are My ways higher than your ways, And My thoughts than your thoughts." Isaiah 55:8

The things God does man will never be able to fathom. 
Gods ability to forgive is immeasurable in comparison to ours. 

 "As a father pities his children, So the Lord pities those who fear Him." Psalms 103:13
God's concern for us is a parental concern.

"For He knows our frame; He remembers that we are dust. As for man, his days are like grass; As a flower of the field, so he flourishes." Psalms 103:14 
God understands us in all of our sinfulness, and still forgives us. 

The point is this;
The more we look at ourselves the more dissatisfied we become.
But when God looks at us, He understands everything completely, and says "I still forgive you."  
That's the kind of God we have. We may not understand it, but we can still be thankful for it. 

God's forgiveness is rooted in His character, not His plan. God has a plan, and forgiveness is part of that plan for believers, but forgiveness does not come from the plan, it comes from God's character. The purpose of God's plan is to teach us His character.