On April 21, the second night of Passover, Jews across the globe began counting. Counting what? The Omer (in Hebrew sefirat ha’omer). The counting will continue for 49 days, seven complete weeks, until Shavuot, the “Festival of Weeks.”
Why do we count? First, to demonstrate our excitement for the impending occasion of receiving the Torah, the occasion we mark on Shavuot.
Second, the 49 days are considered a period of spiritual cleansing. When the Jews left Egypt they were morally and spiritually defiled. By the time they stood at the foot of Mt. Sinai, they were pure, likened to angels. It was during this 49-day period they underwent this radical transformation.
Each year we are supposed to consider Shavuot as if we are getting the Torah anew. And each period of counting could be looked at as a chance to metaphorically cleanse ourselves. It is a chance to shift from stagnantly following Jewish rituals to deepening our connection with God and the Torah.
Counting the Omer is a mitzvah, so a blessing is said before counting. However, if you missed any of the nights, you are supposed to omit the blessing, listen to someone else who has counted each night say it, and then count with him or her.