Common grace

In a fallen world, how is it that unbelieving men and women are capable of great acts of kindness, can experience a measure of joy and happiness, and possess wonderful skills and talents? Why does God cause "his sun to rise on the evil and the good, and sends rain on the righteous and the unrighteous" (Matthew 5:45)? The doctrine of common grace powerfully explains the world we live in and how we should act towards unbelievers.