"The apostles committed their doctrine to writing from these considerations, for these reasons, and for this use: (1) that they might repeat in writing what they had personally delivered orally, and recall it to memory; (2) that they might explain by means of epistles those things which were to be built on the first elements of faith which they had transmitted; (3) that the churches were being disturbed and the doctrine adulterated under the pretext and title of traditions supposedly received from the disciples; (4) that the doctrine received from the apostles by word of mouth was not being faithfully preserved by tradition; (5) that other teachers that were not apostles might have the written testimony from which they could prove to the churches that the doctrine which they brought was apostolic; (6) that the church which could not hear the living voice of the apostles might be certain which doctrine they were to receive and venerate as truly apostolic; (7) that the apostles afterward laid down in writings the same things which they had delivered orally while they were present; (8) that in the writings of the apostles there is present not merely a bare catalog of the chief points of apostolic doctrine but also adequate explanations; (9) that the rule of the Christian faith should be in the Scripture; (10) that it might be possible to know from the writings of the apostles what knowledge they had concerning the mystery of Christ; (11) that the apostles wrote in this way that the believers might be able, in the infirmity of this life, to grasp the mysteries of the gospel; (12) that after having committed to writing the same things they had previously transmitted, they might preserve the purity of the doctrine against corruptions; (13) that the apostles comprehended in their writings both the first elements of faith and the fuller and more complete teaching which followed later; (14) that all Scripture given by inspiration of God is profitable so that the minister of the gospel may be complete, equipped for every good work of the ministry; (15)  that the apostles wrote to this purpose, that the church, after it was deprived of the voice of the apostles through their death, might have the means by which it could retain and preserve the memory of the apostolic doctrine, especially because in the last times many errors would be foisted upon the church by means of words which would parade under the name of apostolic traditions; (16) that there would be a model, showing how a minister must conduct himself in the church, in order that the church may be and remain a pillar and bulwark of the truth; (17) that the apostles afterward wrote the same things which they delivered from the beginning, and this for confident use by people of every age, in every church, and for all time to come; (18) that they wrote both for those who believed already and for such as were yet to come to faith; (19) that they received the command to write from the Son of God Himself; (20) that the origin, cause, and use of the Scripture in the New Testament is the same as the Old Testament, so that nothing would be added, nothing taken away, and nothing be departed from either to the right or to the left."  

Martin Chemnitz, Examination of the Council of Trent