One of the "new" approaches to Tanach study today is the use of literary tools and analysis to help us better understand the Torah itself. This is not really a new method - though it had fallen into disuse over the centuries - as its origins date to the Torah itself.
"Write down this song and teach it to the Jewish people" (Devarim 31:19) is the last of the 613 mitzvot, obligating each one of us to write or commission a sefer Torah[1]. This sefer the Torah tells us is a shira, a poetic song that can only be properly understood by those who have an understanding and appreciation of literary techniques. We have often made note of the Netziv's fascinating introduction to his commentary of the Torah where he most beautifully explains how the Torah follows the rules and techniques of poetry even as it may look like prose (see here for example).
While literary tools can give us a much greater appreciation of the Torah they also have legal implications. A quick perusal of the 13 hermeneutical principles of Rabbi Yishmael which teach us how to read between the lines of the Torah indicate the importance of form and not just substance. Whether the Torah first records a general principle followed by an example or vice versa has major legal implications.
The most "radical" of these literary/legal devices is the gezerah shava where the mere fact that the same word appears in two different places allows us to apply the law as specified in one instance to the other instance where no such law is specified. This is so even if the parallel words appear in two very different contexts.
Due to the potential for abuse of such a tool - after all similar words appear all over the place - the application of this rule is limited so that "a person may not adjudicate a gezerah shava on his own." Rather one may use a gezerah shava only if there is long standing tradition to do so. Common words alone are not enough.
Apparently our tradition saw significance in common words where a thematic connection existed between them. Such would help explain the opening lines of the Gemara of masechet Kiddushin. The opening Mishna teaches that one can be mekadesh, betroth, a woman in one of three ways: through money, which includes a monetary equivalent such as a ring; by use of a sh'tar, legal document; or through biah, sexual intimacy. Of the three only the last is specifically mentioned in the Torah - as the Gemara notes "these [kesef and sh'tar] are for the purpose of biah" (Kiddushin 2b).
The Gemara explains that we derive the effectiveness of kesef[2] as a means of kiddushin from "kicha kicha from the field of Efron." The one Biblical verse that speaks of marriage begins "ki yikach, when a man takes a woman". The same phrase yikach[3], is used by Abraham's purchase of a burial plot for Sarah from Efron. And since by Abraham's purchase of the land the Torah specifies it was "taken" with money, so too when the Torah uses the term "yikach, to take" by marriage it teaches that money can be used as the medium.
Why one needs a rabbinic tradition to do this should be most clear. Left to my own devices I may have used a gezerah shava from the story of Korach where we are told "vayikach Korah, and Korach took. Perhaps we can argue just like Korach "took" his collaborators with words so too one can marry by words alone. Or perhaps we might argue that one must light a fire to get married based on the fact that Nadav and Avihu "took" a pan of incense into the Temple.
Our Sages were not interested in word play alone. As Rav Shimshon Rapahel Hirsch explains our tradition purposely linked marriage and death. When one stands under the chuppah one commits to one's spouse "till death do as part" and beyond, as demonstrated by Abraham's tremendous efforts and expense to ensure a proper burial for his wife. Marriage and death may be contradictory notions but reflect the cycle of life and even more importantly the eternity of the Jewish people. At our happiest moment we must be cognizant of the temporary nature of individual life and the eternity of the Jewish people. Death does not deter us from creating life and it is not coincidental that immediately after the death and burial of Sarah the Torah spends sixty-seven long and repetitive verses detailing the marriage of Yitzchak to Rivka. We may physically die but those who create kiddushin, holiness, continue to live on.
Vkesef minalan the Gemara asks. From where do we know that kesef can be used to effect kiddushin? For some people money is the root of evil often leading to dissension. For others money is a mechanism to bring people together, to create holiness. That is the goal of marriage, the central topic of masechet Kiddushin.
[1] With the Torah clearly stating that the purpose of the mitzva is so that we may be able to [learn and] teach Torah the Shulchan Aruch, (Yoreh Deah 270:2) quoting Rabbeinu Asher rules that one fulfills the mitzva today by acquiring a Jewish library.
[2] Strangely the Gemara's concern is not the source for kesef as a mode of kiddushin but rather the use of the term "niknet" to acquire. The Torah in describing monetary purchases uses the term yiknoand since our Mishna also uses kesef it too makes use of a similar term niknet. Knowing why kesef is a valid means is almost an afterthought.
[3] What makes this gezerah shava even more unusual is that unlike most other cases we are not even using the same word, but rather a word with a similar root. Whereas by marriage the word used is yikach, by Abraham the word uses is kach.
