However, Jacob Neusner argues that the Mishnah does far more than expound upon and organize the Biblical commandments. Rather, important topics covered by the Mishnah "rest on no scriptural foundations whatsoever," such as portions of the civil law tractates of Bava Kamma , Bava Metzia and Bava Batra .  In other words, "To perfect the [Written] Torah, the Oral tradition had to provide for a variety of transactions left without any law at all in Scripture."  Just as portions of the Torah reflect (according to the documentary hypothesis ) the agenda of the Levite priesthood in centralizing worship in the Temple in Jerusalem and legitimizing their exclusive authority over the sacrificial cult, so too can the Mishnah be seen as reflecting the unique "program" of the Tannaim and their successors to develop an egalitarian form of Judaism with an emphasis on social justice and an applicability throughout the Jewish diaspora.   As a result, the Talmud often finds the rabbis combing scripture for textual support to justify existing religious practice, rather than deriving the practice organically from the language of scripture. 
Why do these stories and these oral traditions finally get written down is the question.... Perhaps because in order to communicate from one community to the other. The only way in which different Christian communities who had contact with each other could assure that their traditions were uniform and could be shared was by writing them down, and by thus exchanging those stories. It could also be written down in order to be used as letters of recommendation. Now let me explain this because this sounds a little strange. We do know that Christian apostles traveled around not only doing miracles, but also bringing records of miracles they had done at other places and at the same time miracles of Jesus they had written down in order to be used as accreditation as they came to a new community....
Notes on the Pauline Letters:
* 1 Tim, 2 Tim, Titus are usually called the "Pastoral Letters" since they are addressed to leaders or "shepherds" of Christian communities.
* Eph, Phil, Col, Phlm are sometimes called "Prison Letters" since Paul apparently wrote them while in prison (Eph 3:1; 4:1; Phil 1:7, 13-14; Col 4:3, 10; Phlm 9-10).
* Rom, 1 Cor, 2 Cor, Gal, Phil, 1Thess, Phlm are often called the "Undisputed Letters," since most scholars agree they were written by Paul himself.
* Eph, Col, 2 Thess, and 1 Tim, 2 Tim, Titus are often called the "Disputed" or "Deuteropauline Letters," since many scholars believe they were written by Paul's followers after his death, rather than by Paul himself; but scholarly opinion is divided, with some scholars arguing for their authenticity.