Kommentar zu Wajikra 23:21

חקת עולם לכל מושבותיכם, even though no manner of sacrificial offering could be offered in any of the countries to which Jews were eventually exiled, the “counting” part of this legislation would not be abandoned on account of this.

וקראתם בעצם היום הזה מקרא קדש, “and you will proclaim a holy convocation on this very day.” The reason why the Torah does not spell out in which month this occurs, and on what date of this month, as it does with all the other festivals, is if it had done so, the people would not have been counting weeks and days, but would simply have contented themselves with observing the festival on its appropriate date. The counting was an important feature of these weeks as we have pointed out on verse 15. Nowadays, in the absence of the Temple, our being in exile, and having adopted (therefore?) a permanent calendar, the fiftieth day after the first day of Passover automatically occurs on the same date in the month of Sivan, the date on which the Ten Commandments (orally) were given to the Jewish people at Mount Sinai. In light of the fact that the counting is no longer associated with the date of Shavuot as that date was known, the benediction commencing with שהחיינו וקימנו לזמן הזה, “Who has kept us alive and well until this point in time,” is not recited.