B. B. Warfield 
What Is Calvinism; The Meaning & Uses of the Term; Brief Untechnical Statement of Reformed Faith [EPUB ebook] 

It is very odd how difficult it seems for some persons to understand just what Calvinism is. And yet the matter itself presents no difficulty whatever. It is capable of being put into a single sentence; and that, on level to every religious man’s comprehension. For Calvinism is just religion in its purity. We have only, therefore, to conceive of religion in its purity, and that is Calvinism.In what attitude of mind and heart does religion come most fully to its rights? Is it not in the attitude of prayer? When we kneel before God, not with the body merely, but with the mind and heart, we have assumed the attitude which above all others deserves the name of religious. And this religious attitude by way of eminence is obviously just the attitude of utter dependence and humble trust. He who comes to God in prayer, comes not in a spirit of self-assertion, but in a spirit of trustful dependence. No one ever addressed God in prayer thus: ‘0 God, thou knowest that I am the architect of my own fortunes and the determiner of my own destiny. Thou mayest indeed do something to help me in the securing of my purposes after I have determined upon them. But my heart is my own, and thou canst not intrude into it; my will is my own, and thou canst not bend it. When I wish thy aid, I will call on thee for it. Meanwhile, thou must await my pleasure.’ Men may reason somewhat like this; but that is not the way they pray. There did, indeed, once two men go up into the temple to pray. And one stood and prayed thus to himself (can it be that this ‘to himself’ has a deeper significance than appears on the surface?), ‘God, I thank thee that I am not as the rest of men.’ While the other smote his breast, and said, ‘God be merciful to me a sinner.’ Even the former acknowledged a certain dependence on God; for he thanked God for his virtues. But we are not left in doubt in which one the religious mood was most purely exhibited. There is One who has told us that with clearness and emphasis.