For the nation of Israel, the ‘days of the omer’ were a time of great anticipation. The barley harvest began and the wheat harvest would soon follow. They would gather, thresh, and clean grain to store for the next year. For the disciples, forty ‘days of the omer’ were spent with the risen Yeshua; the final ten they waited in Jerusalem for his promise.
http://tentstakeministries.net/2013/04/counting-the-omer-sefirat-haomer-pentecost-shavuot-ruth-naomi/