At the time of yetziat mitzrayim, Benei Yisrael entered into a dual relationship with Hashem. Simultaneously, Benei Yisrael became both avdei Hashem and His kallah. "Ki li benei yisrael avadim avadei hem asher hotzeiti otam meeretz mitzrayim" (Vayikra 25:55), and "Zacharti lecha chessed neurayich ahavat kelulotayich" (Yirmiyahu 2:2). Both of these aspects of our relationship with Hashem reached their fruition at Matan Torah.
In the introductory words to Kabbalat haTorah, the Jewish people are instructed to be an "am segulah." Rashi (Shmot 19:5) understands this to mean "tehiyu kenuyim li"- you should be acquired to me. The Beit Halevi, in his commentary on chumash, elaborates upon this explanation. It is only an eved, who literally sells himself to another, who can be possibly be obligated to fulfill every command of his master. It was only through becoming avadim leHashem that we became obligated to observe all of the mitzvot.
Yet, Matan Torah has another dimension. Rashi (Shmot 19:17) sees in the Har Sinai experience similarities to a wedding. Many customs we observe at a wedding are reminiscent of Sinai, such as lighting candles, symbolic of the flashes of lightening that accompanied Matan Torah. What is the significance of this dual relationship and how does it express itself practically in our avodat Hashem.
The Ramban (Shmot 20:8) observes that the division of mitzvot into positive and negative commandments reflects two aspects of avodat Hashem. Positive mitzvot stem from avodat Hashem a desire to act in a way that will bring you closer to your Beloved. Observance of prohibitions is a reflection of one's yirat Hashem; one refrains out of fear and awe from violating the word of one's Master. The true eved Hashem will never violate a mitzvah lo taaseh and a yedid Hashem - the beloved of Hashem will constantly search for positive ways to draw closer to his Beloved.
The Ramban sees these two parts of avodat Hashem in the dual obligations of Shabbat. Chazal, in Massechet Brachot 20b, interpret the phrase "Zachor et yom hashabbat" as referring to the prohibition of melachah. "Zachor" is an example of a "mitzvat aseh" which stems from ahavat Hashem whereas "shamor", a "lo taaaseh" has its roots in yirat Hashem.
Following the words of the Ramban we can reach a deeper understanding of what Chazal mean. "Zachor veshamor bedibbur echad neemru." Not only does this refer to these specific mitzvot which were recited simultaneously at Har Sinai, but applies to both aspects of avodat hashem that must always go hand in hand. One who perfects his avodat Hashem can potentially reach a feeling of closeness and comfort with Hashem in which he forgets that he is ultimately infinitesimal in relationship to his Creator. Yet, one who strives for perfection in his yirat Hashem may do so at the expense of being able to relate to Hashem with a sense of love and friendship. This is why we are instructed in Pirkei Avot ( 1:3) to serve Hashem out of love yet simultaneously not to forget "yehi moreh shamayim aleichem." Even at a time of love one must be in awe of Hashem.
The perfection of these two aspects of avodat Hashem- ahavah veyira, eved veyedid, is our goal on Shavuot and throughout the year. May we always reach this perfect blend of "Zachor veshamor bedibbur echad neemru."