The doctrine of reprobation acts as a hinge upon which the entire doctrine of God’s sovereignty in salvation turns. If He chose some for salvation, then He must have chosen not to save others. To deny that God chose not to save some people is to raise the question whether God made any choice at all about whom He would save. One’s view of reprobation functions as a window into his understanding of election. . . .

In his definitive 1559 edition of the Institutes, Calvin unequivocally states: “Election itself could not stand except as set over against reprobation. God is said to set apart those whom he adopts into salvation; it will be highly absurd to say that others acquire by chance or obtain by their own effort what election alone confers on a few. Therefore, those whom God passes over, he condemns; and this he does for no other reason than that he wills to exclude them from the inheritance which he predestines for his own children.”

Joel R. Beeke, Debated Issues in Sovereign Predestination: Early Lutheran Predestination, Calvinian Reprobation, and Variation sin Genevan Lapsarianism, 83-84.