Calvin's system was modelled to a great extent on the doctrines of Luther and Zwingli, but it was coloured largely by his own harsh and morose disposition. For the distinguishing feature of his system, namely, absolute predestination, he was dependent largely upon the works of Wycliffe. Like Luther, he began with the assumption that the condition of man before the Fall was entirely natural, and that consequently by the Fall he was deprived of something that was essential to his nature and without which human nature was completely corrupted. Man was no longer free, and every act of his was sinful. His want of freedom was the result of the play of external forces directed and arranged by God, rather than of any internal necessity by which he was forced to sin. God is, according to Calvin, the author of sin, in the sense that he created a certain number of men to work evil through them in order that He might have an opportunity of displaying the divine attribute of mercy. Hence the motive of God in bringing about evil is different from the motive of the sinner, and therefore though the sinner is blameworthy God is nowise responsible for his crime. Adam sinned because it was decreed by God that he should fall in order that the divine mercy should be manifested to the world. For the same reason God did not intend that all should be equally good or that all should be saved. He created some men that they might sin and that their punishment might afford an example of God's justice, while He made others that they might be saved to show His overwhelming mercy. The former are condemned to hell by an irreversible decree, the others, the elect, are predestined absolutely to glory. The elect are assured of justification through the merits of Christ, and once justified they are always justified, for justification cannot be lost. Faith such as that advocated by Luther was the means of acquiring justification, but, mindful of his other doctrine that even the best of men's works are sinful, Calvin took care to explain that justifying faith was only the instrument by which a man laid hold of the merits of Christ. It was like a vessel which, though containing some priceless treasure, was in itself worthless.