Friday is the 12th day, which is one week and five days, of  the counting of the Omer, the measure of barley that was harvested in ancient times at the end of the 49-day counting period. The blessing over the counting of the Omer is recited at night and is omitted during the day if one forgot to count.

Each day of the Omer is related to a different level of the kabbalistic "Sefirot," the emanations through which the Almight interacts with the world. Each of the seven weeks is associated with one of seven Sefirot, and each day within each of the seven weeks is associated also with one of the same seven Sefirot.