This was written by Reuven’s brother about him:
I would like to propose an insight which might help us understand what happened to our dear Reuven Z”L. Of course we don’t ask questions. Hashem runs the world and we accept whatever He does. But maybe this is something we can learn from this story. Reuven Z”L was a man with sterling Middos. A true Ben Torah. He learned Torah and taught others. He was friendly with those of his stature, as well as those not as gifted as he was. He learned with frum Jews, and those who were on their way. He brought others close to Hashem through osmosis. The chein one could feel, the pleasantness that was felt emanating from him, and the dignity with which he treated every Jew. This is what drew so many to him, and as a result, to Hashem. One of Reuven Z”L’s rebbeim said about him, “He was a walking Kiddush Hashem.”
This is what reuven Z”L was about – bringing glory to Hashem’s name. Reuven Z”L’s last Mitzvah, his last act, was one of dedication to his talmidim. He was always devoted to them, as well as to his family. It was an act of Kiddush Hashem, and it brought about a worldwide Kiddush Hashem. The Mishna in Pirkei Avos says that if someone desecrates the name of Hashem in secret, Hashem punishes him publicly. The same is true on the flipside. If a person sanctifies the name of Hashem in secret, Hashem rewards him publicly. Throughout Reuven’s life he was mekadeish Sheim Shamayim in a very quiet, unassuming manner. Maybe that is why Hashem gave him the opportunity to complete his mission with an act that would cause a public Kiddush Hashem, one which would spread all across the globe.
The Mishna in pirkei avos says that the reward for a mitzvah is another mitzvah. Maybe we could say that Hashem rewarded Reuven Z”L with this glorious opportunity to do a huge mitzvah of a public kiddush Hashem, and B”H he grabbed it.