This week the mourning customs associated by tradition with the period between Pessah and Shavuot, Sefirat Ha'omer, are suspended either temporarily or completely - depending on the minhag (custom) of the group - by Lag Ba'omer - the 33rd day of the counting of the Omer. Both the mourning practices themselves and the celebration of Lag Ba'omer are strange phenomena in the Jewish calendar. It is not at all clear how they originated or why. Certainly the Torah knows nothing of them. "And from the day on which you bring the sheaf (omer) of elevation offering - the day after the Sabbath - you shall count seven weeks. They must be complete; you must count until the day after the seventh week - 50 days; then you shall bring an offering of new grain to the Lord" (Leviticus 23:15-16). This seems to be a simple injunction to mark off a specific period of time, seven weeks, between the beginning of the harvest season at Pessah and its conclusion at Shavuot. There is also a parallel here to the celebration in the autumn season when we have seven days of Succot and conclude with a sacred gathering - Atzeret - on the eighth day. Here it is seven weeks rather than seven days and the Atzeret is Shavuot. Certainly there is nothing sad connected to this injunction. Three suggestions have been offered concerning the mourning practices. One is simply that since we can no longer bring the omer due to the destruction of the Temple, the practice of counting is in remembrance of the Temple and its destruction (Menahot 66a) and therefore we mourn. Of course in that case we should be in perpetual mourning, since every day we recall in our liturgy the sacrifices that we can no longer bring. The commentator Abudarham has suggested that the mourning stemmed from the popular and justified fear that something could go wrong with the harvest. If there would be rain, storms or some other climate disruption, all could be lost. Thus a dark hue was cast over this period of time as everyone waited anxiously for the outcome of the harvest. Under such conditions celebrations would be inappropriate. The Talmud offered a historical reason. It speaks of the death of 12,000 of Rabbi Akiva's students during that period of time "because they did not treat one another with respect" (Yevamot 62b). Although one authority in the Talmud speaks of a plague as the cause of their deaths, some historians have suggested that underlying this story is a struggle against the Romans rather than an illness. Both of the sages whose names are connected with this period of time, Rabbi Akiva and Rabbi Shimon Bar Yohai, are known for their active opposition to the Roman authorities. Both placed themselves in danger because of this and, as is well known, Akiva was martyred for it. There is a tradition that the deaths of these students ended at Lag Ba'omer, thus explaining both the mourning and the interruption. In our own time the placement of Holocaust Remembrance Day during the Sefira period gives new meaning to the sadness associated with it. The Committee on Jewish Law and Standards of the Rabbinical Assembly has ruled that the public mourning practices, which are in any case of doubtful origin, need be observed only until Holocaust Remembrance Day. I believe that Sefira can also have a positive side to it. Since in the Torah Shavuot is given no historical explanation, Sefira originally was connected only to the harvest, to agriculture. However for thousands of years rabbinic tradition has declared that Shavuot is the anniversary of the giving of the Torah. Therefore I would like to suggest that the counting of the days between Pessah and Shavuot should be seen in a different light - as anticipation of God's revelation, a counting up in the spirit of ma'alin bekodesh - going up in holiness. Pessah marks our birth as a nation, as a people. Without it we would not exist. Therefore it is the primal event in our history and is mentioned and celebrated as such over and over. Shavuot, however, marks our transformation into a holy people. In the words of the Torah spoken by God before the revelation at Sinai, "Now then, if you will obey Me faithfully and keep My covenant, you shall be My treasured possession among all the peoples. Indeed all the earth is Mine, but you shall be to Me a kingdom of priests and a holy nation" (Exodus 19:5-6). The journey from Pessah to Shavuot, this period of seven weeks, is a time of transformation and dedication to the purpose of our existence. We emerged from Egypt, from slavery, not only in order to be free but also in order to dedicate ourselves to the service of God. "They are My servants whom I freed from the land of Egypt..." (Leviticus 25:42). Therefore we count each day in anticipation of that great event when we will complete our transformation into a holy nation, dedicated to creating a society in which the will of God will be manifest. As we count each of these days, we elevate ourselves so that we will be worthy of standing at Sinai and entering the covenant. The writer is the head of the Rabbinical Court of the Masorti Movement and the author of several books, the most recent being Entering Torah.