All his pamphlets were couched in popular language and were exactly the kind of works likely to appeal to the masses of the people, as well as to the debased instincts of those who had entered into the religious state in response to the wishes of their parents or guardians rather than in obedience to the call of God. But while Luther thus catered for the multitude, Melanchthon sought to gain the support of the more educated classes by throwing Luther's teaching into scientific and systematic form in his work, /Loci Communes/ (1521), a book that remained for centuries the standard authority on Lutheran teaching. It would be wrong to assume that Luther developed his theological system in its entirety before his separation from the Church. On the question of Justification and Free-will he had arrived at views distinctly opposed to Catholic doctrine, but his system as such took shape only gradually in response to the attacks of his opponents or the demands of his friends. On the one hand, imbued with the ideas of German Pantheistic mysticism, Luther started with the fixed principle that man's action is controlled by necessary laws, and that even after justification man is completely devoid of free will at least in religious matters. According to him, human nature became so essentially maimed and corrupted by the sin of Adam that every work which man can do is and must be sinful, because it proceeds in some way from concupiscence. Hence it is, he asserted, that good works are useless in acquiring justification, which can be obtained only by faith; and by faith he understood not the mere intellectual assent to revealed doctrines, but a practical confidence, resulting, no doubt, from this assent, that the merits of Christ will be applied to the soul. Through this faith the sinner seizes upon the righteousness of Christ, and by applying to himself the justice of his Saviour his sins are covered up. For this reason Luther explained that justification did not mean the actual forgiveness of sin by the infusion of some internal habit called sanctifying grace, but only the non-imputation of the guilt on account of the merits of Christ.