Sorry for the simpleness of this question. I've been trying to study the Torah as much as possible. I do not know Hebrew (though I'd truly like to and would appreciate any advice on how to get started), but when I want to talk about the law I see that there are a lot of references to different Rabbis. I'm not - unfortunately - familiar with writings of different Rabbis. My question is why do I see so much referring to writings of Rabbis, and is it necessary to 'quote' what a Rabbi said about a particular subject in order to discuss the Torah?
HodofHod gives a pretty good example and explanation as to why our tradition is important, but I'll try to expand on that a bit to explain what the tradition is and where it comes from (and explain it in a bit more of a straightforward way).
Judaism relies heavily on generation-to-generation, teacher-to-student, parent-to-child tradition. This is known as Mesorah, which means "Passing", as in passing learned wisdom from one person to the next, as one would pass a torch in the Olympics.
Our tradition teaches us that when G-d gave the Torah to the Israelites, they were given both a written Torah and an oral Torah. That is to say, neither is complete without the other. Just as HodofHod wrote, you cannot understand parts of the written Torah without some input from the oral Torah. If you were to try to explain, for example, how to create the "Totafoth" as commanded in Deuteronomy 6:8 it would not be difficult, it would be impossible - without the oral Torah. G-d told Moshe (Moses) to write down the basic law, but then He taught him how to apply it; this is, on its most basic level, what the oral Torah is. It's the part of the Mesorah that allows us to understand what G-d was saying in the Torah He gave to us.
Part of our Mesorah is also a set of principles for interpretation, which is itself very important, because there are areas of life that are, naturally, not explicitly discussed in detail in the Torah.
The above is to serve as background to answer your question directly:
Why do we reference the sayings of earlier rabbis when interpreting the Torah?
Because they are the ones who have served as the links in the chain of our Mesorah.
That is not to say that one cannot interpret the Torah, and in fact the Talmud is a vast collection of discussions and debates among the ancient rabbis based on their interpretation. In addition, the Midrash (a vast collection of interpretations from ancient rabbis) tells us that there are 70 faces to the Torah. But what it means is that we have a rock-solid tradition stemming back, literally, from teacher to student, since Moshe received the Torah directly from G-d, that cannot be done away with just because someone thinks the law should be different. When one innovates, if he does so correctly, he uses the techniques that have been used for millennia, and he contends with the traditional interpretation using those same techniques - and, perhaps most importantly, he does so with great deference and respect for the interpretation that has been accepted, and with those who disagree with him. Famously, Rabbi Shlomo Zalman Auerbach, a 20th Century rabbi in Israel, was known to have said that if it weren't for the fact that those who preceded him banned the active use of electricity on the Sabbath, he would have said it was permissible. Because of his reverence for those who came before him who saw the issue differently, he upheld their ruling because it was based on their interpretation of the laws of the Sabbath as applied to the then-new phenomenon of harnessing electricity to power devices in our daily lives. Although he disagreed, and indeed he was very innovative in his approach to applying the Torah to modern life, he did not overrule them because of the importance of adhering to the traditional approach to interpreting and following the Torah through the lens of Mesorah.
tl;dr: You need the Rabbis' commentaries to understand the Torah correctly.
The Torah is a book that cannot be understood (and was not meant to be) unless you also have the oral teachings that came with it when it was given. These teachings were passed down verbally, until the times of Rebbi, who compiled many of the different traditions of the Oral Torah into the book called the Mishnah. Additionally, Rabbis who are familiar with the entire Torah and the Oral Torah, can make correlations and learn new things that were not passed down (provided that their methods are valid).
[Insert the history of Judaism here]
Since then, Rabbis have continued learning and passing down their traditions and insights through the generations. Learning the Torah without the commentary of the Rabbis, is (l'havdil) a little like reading the Constitution without the laws and legal decisions made since then, and without understanding the men who wrote it, and the society they lived in.
To give an example: The foremost Rabbi who comments on the Torah, is Rashi. Rashi's work is nearly all made up of quotes from earlier Rabbis. Rashi compiled thousands of different sources and traditions of Torah's meanings, and wrote them down by chapter and verse. Without Rashi, you get to passage like Exodus 21:24:
an eye for an eye, a tooth for a tooth, a hand for a hand, a foot for a foot,
..and you think, "Does the Torah actually mean that you should gouge out someones eye?" No! The Oral Torah that was passed down from the times of Moses explains, so Rashi brings it down for us:
an eye for an eye: If [a person] blinds his neighbor’s eye, he must give him the value of his eye, [which is] how much his price to be sold in the marketplace has decreased [without the eye]. So is the meaning of all of them [i.e., all the injuries enumerated in the following verses], but not the actual amputation of a limb, as our Rabbis interpreted it in the chapter entitled הַחוֹבֵל, he who assaults. -[From Baba Kamma 83b, 84a]
The fact that someone lived in an earlier generation does not make his opinion better than mine. Nor does the fact that someone is a great rabbi imply that he is a super genius whose opinions are inherently wiser than anyone else's. But just as with any profession if you want to know the answers you go to the pros, so it is with Torah. A Rishon doesn't have more of a say than I do. But Rashi, the Rambam and the Rashba and for that matter my own rabbi are much more proficient in Torah than I am. They've gone through it all. That is why I generally value their opinion over my own, inasmuch as I value my doctor's opinion over my own when it comes to questions that require medical expertise. And I'm sure you would rather hear the opinion of a professional than that of an amateur, which is why if you ask me a question it is likely that I will try to cite some of the great rabbis instead of simply presenting my own theories.
In support of the idea that an earlier opinion is not better per se than a later on, see R. Ovadia Yosef in his introduction to Halichos Olam, where he writes as follows:
וכמש"כ הגר"ח מוואלוזין בשו"ת חוט המשולש (סי' ט) בזה"ל: ואע"פ שאנכי שמשתי את מו"ר הכהן הגדול ומחוייב אני בכבודו ובמוראו כמורא שמים, מ"מ אני שומר מה שאמרו חז"ל (ב"ב קל:) כד אתי פסקא דדינא קמייכו וחזיתו ביה פירכא לא תגמרו מיניה, שאין לדיין אלא מה שעיניו רואות. וכבר הוזהרתי מפי מורי קדוש ישראל הגר"א מווילנא שלא לישא פנים בהוראה. וכ"כ עוד בספרו רוח חיים (פ"ד דאבות מ"ד) שאסור לתלמיד לקבל דברי רבו כשיש לו מה להשיב עליהם. כי לפעמים תהיה האמת עמו. כמו שעץ קטן מדליק את הגדול. ע"ש. וע"ע להגר"ח פלאג'י בשו"ת חקרי לב (חיו"ד סי' מב), שאין לת"ח לכבוש את נבואתו בפסקי הלכה, וחייב לגלות דעתו, ונכתב בספר, שאין משוא פנים בדבר. ומרן הקדוש בספר אבקת רוכל (סי' קנה) כתב וז"ל: ואע"פ שהריטב"א והריב"ש בקיאים יותר בפירוש דברי הראשונים, מ"מ במילתא דאיכא טעמא ואיכא למותיב מותבינן דלאו קטלי קני באגמא אנן. ע"ש. ובשו"ת נודע ביהודה קמא (חאו"ח סי' לה) ד"ה ומה, כתב, ואף שבתשו' חות יאיר פסק להיפך, אטו כל מקום שמצאנו הלכה בתשובות האחרונום נחליט כן לדינא, הלא חיך יטעם אוכל. ע"כ. וע' בשו"ת רבי ישעיה הראשון (סי' סב) שכ', ומ"ש מר שלא אחלוק על הרב הגדול רבינו יצחק בעל התוס', חלילה לי מעשות זאת, והגם כי מה אני נחשב לפניו, אך זאת אתי, שכל דבר שאינו נראה בעיני, אפילו אי אמרה יהושע בן נון לא צייתינא ליה. ואיני נמנע לומר הנראה לי לפי שכלי, ואדברה בעדותיך נגד מלכים ולא אבוש, וכמשל הפילוסופים בננס על גבי ענק. ומעולם לא נמנעו האחרונים מלסתור דברי הראשונים, וכמה משניות סתרו האמוראים לומר שאינם הלכה, ואין חכם שיהיה נקי משגיאות