Our sages tell us that all material matters stem from a spiritual root. In other words, this "real" world we inhabit is an expression of a spiritual world. Through our actions, we have the capacity to affect the spiritual world and, consequently, modify the material world. That, ultimately, is the difference between a living person and a deceased person: their capacity to effect change through a mitzvah in this material world.
One might wonder what the relationship is between a mitzvah commanded by the Torah and the spiritual world, since most mitzvot involve physical objects, such as wool, leather, food, etc. The answer is that God's very commandment—that His will is for us to do such and such—connects the material aspect of human action with the spiritual realm.
That is why our sages say, "A single moment of repentance and good deeds in this world is better than a lifetime in the world to come," since there is no possibility of growing there as much or in the same way that we can here. From this arise other similar thoughts, such as, "If not now, when?", or "Repent before you die," or simply, "Don't put off until tomorrow what you can do today.".
However, there are special people, whose souls are special, and who have an even greater influence in death than in life. Like a Rebbe.
The third of Tammuz (Tuesday the 15th) marks another anniversary of the passing of the Lubavitcher Rebbe, Rabbi Menachem Mendel Schneerson, of blessed memory. The Zohar, a fundamental work of Kabbalistic wisdom, says of people like the Rebbe that their presence is felt in all worlds (including this physical world) even more than in life.
The reason for this is very simple: even in life, the life of a person like the Rebbe consisted of love for God, fear of God, and faith in Him.
We all have matters in life that we consider primary and others secondary. There are matters that, despite being secondary, become fundamental, such as eating, drinking, sleeping, etc., which the Torah itself commands us to do (in a particular way, such as kosher, with limits, etc.), but they are still secondary compared to other matters. Certainly, each of us, at our own level, if we could rid ourselves of secondary matters in life and dedicate ourselves only to the primary ones, we could be much more efficient and develop those matters with greater strength.
That is what happens when a Rebbe passes away: everything related to the physical life of the body ceases, allowing him to dedicate himself exclusively to what was primary throughout his life. And since even in life his existence consisted of spiritual matters, when the body separates from the soul, all that occurs is an intensification of those spiritual qualities for which he worked throughout his life. There are no more physical impediments to spiritual growth and development.
That is why its influence increases even in this material world: it is no longer limited by time and space.
Those who study and experience his teachings can receive from the Rebbe strength to serve God from all the spiritual work that the Rebbe accomplished during his life.
The only thing left to think about and resolve in each person's life is: what are my primary concerns and what are my secondary ones? Will there be anything in my life that continues and grows stronger after I leave this world?