Why did the Vilna Gaon cry before he died, with a Tzitzit in his hands?

They tell of the Vilna Gaon who, prior to his death from this world, held the tzitzis on his garment and began to weep bitterly. His disciples asked him: Rabbi, why are you crying? After all, you are expecting a great reward in the World to Come and what are you afraid of?

Rabbi Eliyahu of Vilna told them, “I will explain to you why I am crying.”

Today I am here in this world, where I can observe mitzvot and accumulate more and more rights. I can buy tzitzis, wear on my body this garment, and fulfill every mitzvah so precious that the reward for it is enormous, inconceivable in the human mind. Now, in a few days I will die and be rid of this world, and I will no longer be able to fulfill this precious commandment. How can I not cry?

The commandment of Tzitzit is mentioned several times in the Torah, and in one of them it is brought at great length, when the Torah commands us to tie tzitzit in every garment that has four wings.

It is forbidden to wear a garment with four edges and corners without a tzitzit, for example, if you decide to make a hole in a towel and wear it, you will have to thread it. In principle, the commandment of tzitzit applies only to the extent that we wear a garment of four corners, and then we have the obligation to thread it. However, because of the love of our mitzva and our love for the Creator of the world who gave us the Torah, we try to wear a garment of four corners at all times, and thus fulfill the important commandment – Tzitzit.