The Exodus from Egypt serves as the basis for numerous mitzvot and for one of the fundamental principles of our faith. The first of the Ten Commandments links the belief in God with His having freed us from Egypt. Twice daily we are obligated to acknowledge our indebtedness to God by recalling the Exodus at the conclusion of the Shema. In fact, R. Chaim Soloveitchik zt"l explains that according to the Rambam, the mitzvah of zechirat yetzi'at mitzrayim (remembering the Exodus from Egypt) is not an independent obligation, but is rather an inherent part of the Shema, and as such is a component of our kabbalat ol malchut shamayim (acceptance of the yoke of heaven).
Even our observance of Shabbat is tied to the Exodus. Unlike the Ibn Ezra, who explains the verse, "You shall remember that you were slaves in Egypt" (Devarim 5:14), as commanding that even slaves refrain from work on Shabbat, the Rambam and the Ramban explain this reference as a basis of shemirat shabbat generally. In this sense, the Talmud (Pesachim 117b) insists that we incorporate the theme of yetzi'at mitzrayim into the text of kiddush. Accordingly, the Minchat Chinuch (mitzvah 31) asserts that although many rishonim maintain that any need for wine during kiddush is only mi-derabanan, one would certainly not fulfill the Torah obligation of kiddush with tefillah alone, for nowhere in the shabbat evening amidah of do we mention the theme of yetzi'at mitzrayim.
Even the thirty-nine melachot themselves are linked to the Exodus from Egypt. Tosafot (Pesachim 117b s.v. le-ma'an) cite the Midrash which states that on Shabbat we demonstrate our freedom by abstaining from the various forms of labor that we performed while slaves in Egypt.
Although yetzi'at mitzrayim plays such a central role in our belief, it would be incorrect to view this event as an end in itself. When Moshe Rabbeinu expresses his doubt as to his worthiness of taking the Jews out of Egypt, God assures him that the fact that the Jews would later receive the Torah makes the Exodus worthwhile (see Shemot 3:12). The very purpose and challenge of yetzi'at mitzrayim is to channel this newfound freedom toward the service of God. The Ramban explains that the essence and purpose of sefirat ha-omer is to link the experience of yetzi'at mitzrayim with that of kabbalat ha-Torah. The Ramban comments that the days of Pesach are to be viewed as the first days of yom tov and the days of Shavu'ot as the last days of yom tov, with the intermediate days of sefirat ha-omer serving as a form of chol ha-mo'ed. For this reason the rabbinic literature often refers to Shavu'ot as "Atzeret," the true and fitting conclusion of Pesach. Accordingly, R. Ovadiah Yosef (Yechaveh Da'at 1:24) argues that although the days of sefirah mark the tragic passing of the students of R. Akiva (see Yevamot 62b), it would be incorrect to consider this period as one of aveilut. Essentially these are days of great joy in anticipating kabbalat ha-Torah. Perhaps it is for this very reason that the Torah makes no mention of the mitzvah of simchah on Pesach. Only on Shavu'ot, when the true purpose of yetzi'at mitzrayim is realized, does the Torah obligate us to rejoice.
In this sense, the Aruch ha-Shulchan (O.C. 489) explains the view of the Ramban who maintains that the mitzvah of sefirat ha-omer is a Torah-obligation even today. Even without the Beit ha-Mikdash and the minchat ha-omer (the special sacrifice that was made in connection with sefirat ha-omer), the need to link Pesach to Shavu'ot, and thereby to see freedom as a means to further and enhance one's service of God, is as significant today as it was when the Beit ha-Mikdash stood.
Although the special sacrifices of Pesach and Shavu'ot (the minchat ha-omer and the sh'tei ha-lechem, respectively) have much in common, they are nonetheless brought from different grains. Whereas the minchat ha-omer is brought from barley, which the Talmud describes as ma'achal beheimah (food for animals), the sh'tei ha-lechem is from wheat, described as ma'achal adam (food for people). Perhaps this distinction as well can be understood given the link between Pesach and Shavu'ot. The experience of freedom, in the sense of relief from physical service and oppression, is not one which is unique to humanity. Even an animal can sense the removal of a physical burden. Hence, the minchat ha-omer marking this form of freedom comes from ma'achal beheimah. Shavu'ot, however, which challenges us to use this freedom wisely, to ascend in the distinctly human endeavor of acquiring holiness and enhancing our commitment to God, has its sacrifice brought from wheat, ma'achal adam.
Mitzvot which are performed relatively infrequently are generally accompanied by the blessing of shehechiyanu, in which we thank God for allowing us to perform them. Why then is no shehechiyanu recited on the mitzvah of sefirat ha-omer? The Ba'al ha-Ma'or (end of Pesachim) explains that this blessing is only recited on mitzvot that possess qualities of joy When the Beit ha-Mikdash stood, this was true of sefirat ha-omer and certainly the blessing of shehechiyanu was recited. In our time, however, sefirat ha-omer is only a zecher le-Mikdash, devoid of joy, and therefore no shehechiyanu is recited.
According to the Rambam and Rabbeinu Yeruchum, however, who maintain that the mitzvah of sefirat ha-omer is a Torah-obligation even today, other reasons must be given to explain the omission of shehechiyanu. Rabbeinu Yeruchum explains that the shehechiyanu recited on Shavu'ot itself covers the mitzvah of sefirat ha-omer as well. The very purpose of sefirah is to underscore the significance of Shavu'ot. In fact, whereas all other holidays are linked to specific calendar dates, Shavu'ot commences at the conclusion of the sefirat ha-omer. Therefore only after counting these days and successfully bridging the gap between Pesach and Shavu'ot do we recite the blessing of shehechiyanu.
The days of sefirah are indeed days of intense preparation and anticipation. May we be worthy recipients of Torat Hashem.