Christianity was a living religion. The first congregations were dwelling in an atmosphere of enthusiasm. There was a general outpouring of the Holy Spirit. The prophet's words seemed to be fulfilled: "They shall teach no more every man his neighbour and every man his brother, saying: know the Lord; for they shall all know me." Christianity was not a religion of a sacred book, whose dead letter was to be artificially kept alive by learned men. It was a religion of living experiences. Nevertheless, Christianity from the beginning had a sacred book. Jesus and his disciples used the Bible of their people, the Old Testament, and Saint Paul carried it to the Christian communities of gentile origin, which had not known of it before. Christianity could not do without it. If it was necessary to convince Jews that Jesus was the Messiah, how could this be done without arguing from the Scriptures as proof? If the gospel was to be announced to the heathen they would give less heed to the new tidings than to the statement that it was really the most ancient form of religion as attested by this sacred book, which was superior to all the books of poets and philosophers and legislators by reason of its venerable age. Christianity without any hesitation claimed the Old Testament as its own book, its own Bible. Not only was Jesus the content of this book, he was even believed to be its author. It was the spirit of Jesus which dwelt in the prophets and made them seek and search concerning the salvation offered by Christ (I Peter 1 : 10-11). "The prophets having their grace from him, did prophesy unto him," we are told in the so-called letter of Barnabas. So the Old Testament seemed to be a Christian book both in content and in origin, and it was easy enough to add some properly Christian pamphlets, as Saint Paul's letters and some gospels, the Acts and other letters, and some books of revelation. It was as necessary as it was easy, if Christianity was not to lose contact with its proper origin. The New Testament, as we have it now, was not complete at the start. It was a collection of primitive Christian writings, larger in some ways than it is now; on the other hand lacking some of its present elements. Its precise content did not become finally established until a very late period, not earlier than the end of the fourth century.