The Torah—as interpreted by the Talmud—commands Jews to count off the days from the second night of Passover until the holiday of Shavuot. Jonathan Sacks finds great significance in the details of the commandment known as “counting the omer”:
There is the voice of God in nature, and the call of God in history. There is the word of God for all time, and the word of God for this time. The former is heard by the priest, the latter by the prophet. The former is found in halakhah, Jewish law; the latter in aggadah, Jewish reflection on history and destiny. God is not to be found exclusively in one or the other, but in their conversation and complex interplay.
There are aspects of the human condition that do not change, but there are others that do. It was the greatness of the biblical prophets to hear the music of covenant beneath the noise of events, giving history its shape and meaning as the long, slow journey to redemption. The journey has been slow. The abolition of slavery, the recognition of human rights, the construction of a society of equal dignity—these have taken centuries, millennia. But they happened only because people learned to see inequalities and injustices as something other than inevitable. Time is not a series of eternal recurrences in which nothing ever ultimately changes. Cyclical time is deeply conservative; covenantal time is profoundly revolutionary. Both find their expression in the counting of the omer.
Read more on Rabbi Sacks: http://www.rabbisacks.org/counting-time/