The harmony between the two Testaments soon became a leading idea in Christian doctrine. Some heretics, indeed, would not accept the Old Testament. Marcion maintained that it came from an inferior god, while the supreme God, the father of our Lord Jesus Christ, had revealed himself only through his Son. He found a great many contrasts between the Old and the New Testament, and this criticism was supported by pagan philosophers, as, for example, Porphyry. The church, therefore, was most anxious to establish the harmony of the Testaments by any means at its command. Taste varies from century to century; the minute parallelism constructed by some early Christian writers, and evidently much admired by their contemporaries, seems to us rather ridiculous and fanciful. On the other hand, the church was right in maintaining the harmony. The New Testament needs to be explained from the Old Testament; it is open to much misunderstanding when taken apart. There was almost no sense for historical development at that time; the criticism of Ptolemæus, in his famous letter to Flora, where he speaks of several strata of revelation running through the Old and the New Testament, is an exceptional one. For most of the faithful the Christian doctrine was directly looked for and found in the Old Testament; the gospel was contained in every one of its books, from Genesis to Malachi. Unity was conceived as uniformity. This was the system which appealed most to the average Christian mind. And the Bible was open to all Christians, as Harnack has brilliantly demonstrated in a recent publication. The ancient church laid stress upon this publicity and never tried to withdraw the Bible from the people. There was no hidden mystery regarding the Bible. On the contrary, all members of the church were anxiously urged to make themselves as familiar with the Bible as possible. They were supposed to have copies of their own and to read them privately as well as in the congregation. Even when the struggles about the right doctrine began and the heretics sometimes held to the Bible as their champion against the doctrine of the church, the church did not remove the Bible from public discussion. The ecclesiastical party maintained that the Bible was always in favour of the true doctrine; one needs but to know how to read it. Tertullian, it is true, once in the heat of controversy declared that it was no use arguing against heretics from the Bible, but he did it, nevertheless, and so did the other fathers.