From R.C. Sproul's book "The Truth of the Cross"
"When we incur a debt by failing to meet an obligation before God, that debt must be satisfied-that is, the requirements must be met in a satisfactory way. When sin creates enmity and estrangement, the requirements to end that estrangement and bring about reconciliation must be satisfied. When we commit a crime against God, His justice must be satisfied-a payment or penalty must be given or made that satisfies the demands of divine justice, or it will be compromised."