What are the main essences of Calvinism which separate it from the other Protestant denominations?
This is a great question. Calvinism, as you probably know, is from the theology of John Calvin, the great Reformer of the sixteenth century. His theology has several emphases that separate it from other denominations.
First, Calvinism has a strong emphasis on the total depravity of man. They state that people are dead in their sin and therefore cannot save themselves. Ephesians 2:1-3. There is little idea of working for your salvation. In a Calvinist framework, you work out your salvation.
Second, Calvinism believes in something called "unconditional election." God basically predestines people for salvation. Ephesians 1:3.
Third, there is a belief called "limited atonement," which basically states that Jesus came to die for the elect. Sometimes it is called particular atonement.
Fourth, Calvinist believe in the concept of "irresistible grace, " that is once God predestines someone, he or she will come to him in view of his grace.
Fifth, Calvinists believe in the perseverance of the saints, that is, once a person is saved, he or she will persevere to the end.
These points can be seen in the acronym: TULIP. Total depravity, unconditional election, limited atonement, irresistible grace, and perseverance of the saints.
One final distinctive. Calvinists usually believe in the real presence of Christ in the Lord's Supper. They reject the idea of transubstantiation. The third attachment is an outline of a calvinistic view of salvation.