We are in the midst of the Omer period, during which we mourn for Rabbi Akiva's 24,000 students who died during the short period from right after Passover up until Lag BaOmer, the 33rd day of the Omer. This coming Shabbat is the last one this year on which we practice customs of mourning, because next Shabbat is already the eve of Lag BaOmer and therefore we are permitted to shave and the like in honor of the Sabbath.

The Talmud tells us the reason for the deaths of R. Akiva's students: "Because they did not behave with respect towards each other." This can only be understood in the framework of their great stature, just like in the case of the deaths of the two sons of Aharon HaCohen, Nadav and Avihu. The Torah states that the latter were felled "when they came close to G-d" (Vayikra 16,1), and the 19th-century Netziv of Volozhin explains in his classic HaAmek Davar commentary as follows (paraphrased): 

"They sinned when they came close to G-d" – and a sin in G-d's palace is much worse than one who sins outside the palace. That is, they were on a very high level and their sin was similarly on a high level, in that it was 'close to G-d,' and therefore their punishment was immediate and severe." 

The same is true for the students of R. Akiva: There is no doubt that it was only because of their great stature and intense closeness to G-d that their sin was punished so quickly, practically in one fell swoop.  

Why do we continue to mourn over an event that took place so many generations ago? There are plenty of people who have died tragically over these past 2,000 years ago whom we do not mourn today! Why are R. Akiva's students different? 

The answer involves something that is relevant to all generations, including ours. The Gemara says (Yevamot 62): 

"During the time that Rabbi Akiva's students died, the world was spiritually desolate - until Rabbi Akiva came and taught his five students in the south, namely: Rabbi Meir, Rabbi Yehuda, Rabbi Shimon bar Yochai, Rabbi Yossi and Rabbi Nechemiah. These students [who were later ordained and authorized to teach Torah after all the other Sages were executed by the Romans] became the pillars through which the Torah was handed down to future generations – to the extent that until the Sages said that a Mishnaic ruling without the name of a Sage attached to it is from the words of Rabbi Meir. The other students were equally praised – and all of them perpetuated their teacher R. Akiva's teachings."

Let us try to imagine that R. Akiva was not left with only these five students, but also with the thousands who died within one period. Picture to yourself that they would have merited to continue studying and teaching Torah on their very high level! It could very well have been that they would have perpetuated such an amazing legacy of Torah, that the Torah level in our own generation would have been like that of the Baalei HaTosafot [renowned medieval-age scholars of the Talmud]!