One of the striking things about Shavuot is that he Torah provides no exact date for its celebration. It simply pegs its observance to Pesah:
‘And you shall count for yourselves from the day after the day of rest, from the day that you brought the omer of the waving; there shall be seven complete weeks; to the day after the seventh week shall you count fifty days; and you shall present a new meal-offering to God….And you shall proclaim on that very day that there shall be a holy convocation unto you; you shall do no melekhet avodah; it shall be a perpetual statute in all your dwellings, throughout your generations’ (Lev. 23, 15 and 21).
I think it was the Avne Nezer, R. Avraham Bornstein of Sokhochovזצ"ל (though a quick check of his responsa did not elicit a source), who suggested that the sanctity of Shavuot is only indirectly related to the usual calendar. It is actually created by the enumeration of the days of the Omer by the Jews. If they don’t count, there is room to say that the qedushat ha-yom of Shavuot is (at the very least) impugned.
On Shabbat it struck me that since the mitzvah to count the Omer is an individual obligation (i.e. it can’t be performed by someone else on your behalf), then every Jew contributes to the qedusha of Shavuot. The more Jews who count the Omer, the greater will be the sanctity of the holiday. Since Shavuot is זמן מתן תורתנו, it follows logically that the most proper way to prepare for, and to contribute to, the sanctity of Shavuot is to intensify one’ Torah learning beyond the norm. A התמדה drive, as it were, is required. [HT: R. Dovid Lifshitz זצ"ל.]
Especially today, החושש בראשו (ובנשמתו), יעסוק בתורה.