There is a mitzva for us to count 49 days, 7 weeks, between Pesach and Shavuot. In fact, the Torah doesn’t even give us a date for Shavuot, it simply tells us that it is the 50th day after Pesach. Originally this time was the period that we could not eat new wheat. On shavuot they would bring the korban omer, and then wheat grown that year could be eaten.