Written by: Ted Vial
Reformed and Presbyterian Christianity share the classic grand sacred narrative with other branches of Christianity: God created the world out of nothing; God made it good and populated it with plants, animals, and humans, who enjoyed the earthly paradise, enjoyed direct contact with God, and were originally immortal. But the humans, out of pride, rebelled against God, and this sinful act separated them from God, corrupted human nature, subjected them to death, and marred the perfect creation.
Because the offence against God was infinite, but humans finite, there was nothing they could do to overcome the situation in which they had put themselves. Out of love, God became incarnate (was born as a human) in Jesus; Jesus allowed himself to be put to death as a sacrifice that, because made by a being both human and divine (infinite), pays the price for human sin. Those who hear and believe in this act of love know that their sins are forgiven, and they enter again into a closer relationship with God, including direct contact and immortality, not in this world but in the next. This forgiveness is called grace, because it is freely (or gratuitously) given.
Within this grand narrative (there are others in the Christian tradition, but this has been the dominant one), Protestantism has several distinctive plot twists, and within Protestantism, Reformed theology has further distinctive traits. At the core of the beliefs of all of the major Protestant leaders (Luther, Zwingli, and Calvin) is the belief that sin has completely destroyed human nature. There is no step a human can take to earn God's favor, or even to respond on his or her own to God's offer of forgiveness. God makes the offer of grace, and God responds in the individual's reception of it. God does everything.
For all three leaders this is a hopeful message (in fact it is literally good news, the translation of the Greek word "gospel"), because if your salvation were to any extent in your own hands you would certainly fail. God is far more reliable.
Calvin was a first rate systematic theologian, which meant that he worked out all the implications of each key belief and showed how if one starts in one place, one must then believe that certain other things follow. This led Calvin to articulate the doctrine for which he has become most famous, the doctrine of "double predestination." Predestination means that God decided, from before the beginning of time as part of creation, the destiny of everything in the universe, including whether or not an individual will be saved or damned. For many people this seems to make God into a cruel tyrant. For Calvin, however, the more power one attributes to God, the more one glorifies God adequately. Just as important, the more power one attributes to God the safer one feels, since God is far more reliable than humans. It works to our benefit to have our salvation entirely in God's hands. Calvin's dominant image for God is not king or tyrant but father.