Why is it that after Adam and Eve sinned in the Garden and incurred the just penalty of death, they did not immediately die? What enabled them to go on living to enjoy the many of the benefits of life for years afterward (food, marriage, sex, children, etc.)? And why do so many sinners today enjoy those same benefits, even those who will never believe?
In general, we can answer by pointing to grace—a fitting description for every one of God’s blessing, each of which is, by very definition, undeserved. However, because the grace we are talking about here is poured out “on the just and on the unjust” (that is, on both believers and unbelievers—see Matthew 5:45), and since it is of a different kind than the other manifestations of grace we read about in Scripture (e. g. forgiveness of sin, adoption into the family of God, eternal life in heaven—that is, special grace, or graces related to redemption), theologians have found it helpful to distinguish this as common grace. It is common in that it extends to all people without distinction just as the common room at a university is accessible to every student.
As Wayne Grudem succintly defines it in his excellent Systematic Theology, “Common grace is the grace of God by which he gives people innumerable blessings that are not part of salvation.” Berkhof tells us what such grace accomplishes: “[It] curbs the destructive power of sin, maintains in a measure the moral order of the universe, thus making an orderly life possible, distributes in varying degrees gifts and talents among men, promotes the development of science and art, and showers untold blessings upon the children of men.” Thus common grace encompasses not only physical blessings like rain and food and health, but also blessings in the areas of intellect, morality, creativity, society, and religion. Like all grace, all undeserved favor, it is meant to point us to our kind, loving Creator.