Forty-nine days divide Passover from Shavuot. But this seven-week period is not an ordinary one. It is actually a link that binds these two festivals together. Every one of these days is counted in orderly progression. On every one of these forty-nine nights, a Jew recites a blessing (found in the prayer book) and then verbalizes the number of that day. This counting, called “Sefirat Ha’Omer”  (the Counting of the Omer), expresses a Jew’s eager anticipation of receiving the Torah on Shavuot, forty nine days after experiencing the liberation of Passover. This period is a time of personal refinement and introspection in preparation for receiving the Torah

In Leviticus (23:15) the commandment of counting the Omer is stated:
“You shall count .. from the day that you brought the omer as a wave offering.” The omer was a measure (around two quarts) of barley which the Jews brought as an offering on the second day of Passover. This was followed by the counting of the omer, which led into the fiftieth day- the festival of Shavuot. Even after the destruction of the Temple where the omer offering was brought, this tradition of counting the omer continues.