Sinclair Ferguson provides a helpful summary of John Murray’s view of the functions of common grace. I’ve highlighted the various functions that he enumerates.
Common grace is marked by both negative and positive features. It restrains human depravity and its effects. . . . In common grace God also restrains his own wrath. His longsuffering (1 Pet 3:20) and forbearance (Acts 17:30) are expressions of this. Further, God restrains the influence of the evil that entered the world through sin. The disintegration of life is contained: crops grow even in the midst of the thorns and thistles of the divine curse (Gen 3:17). Nature may well be “red in tooth and claw,” but God has graciously placed the fear of man on the animal world to restrain its destructive tendency.
Positively, God has ordained good in the beauty and abundance of creation and among even unregenerate men. Admittedly the Lord blessed the Egyptians for Joseph’s sake (Gen 39:5); but he did bless them! He bestows good gifts on men (Matt 5:44–45). . . . Furthermore, through common grace “Good is attributed to unregenerate men” (ibid.). Admittedly there is paradox in such a statement, but Murray appeals to The Westminster Confession of Faith (16.7) for confirmation of his exposition. . . .
Again, civil government provides peace and order for men. Strife and unrest are inevitable in a sinful world. That there should be any peace is an evidence of common grace.
What, then, is the function of common grace? It is the precondition for special grace, and ultimately the context in which the salvation and glorification of the elect will take place. Common grace provides both the sphere and the materials in and on which special grace operates.
Sinclair Ferguson, “The Whole Counsel of God: Fifty Years of Theological Studies,” WTJ 50, no. 2 (Fall 1988): 271-72.
One of the intriguing functions, mentioned by Ferguson at the end of his quotation, is the service common grace provides as the precondition for special grace. Abraham Kuyper expands on this function:
Without common grace the elect would not have been born . . . . Had Adam and Eve died on the day they sinned, Seth would not have been born from them, nor Enoch from Seth, and no widely ramified race of peoples and nations would ever have originated on earth. On that basis alone all special grace assumes common grace. But there is more. Even if you assumed that their temporal death had been postponed so that the human race could have made a start, but that for the rest sin in all its horror had broken out unhindered, you would still be nowhere. For then life on earth would immediately have turned into a hell and under such hellish conditions the church of God would not have had a place to strike root anywhere. . . . From whatever angle we one looks at this issue, then special grace presupposes common grace. Without the latter the former cannot function.
Abraham Kuyper, “Common Grace,” in Abraham Kuyper: A Centennial Reader, ed. James D. Bratt (Grand Rapids: Eerdmans, 1998), 169.