In the Gemara in Shabbos (153a) Rav tells Rav Shmuel bar Shilas that when he dies, at his Levaya Rav Shmuel should, "Achim B'Hespeida D'Hasam Ka'imna" arouse the people to tears because Rav will be standing there. What does it mean that Rav will be standing there and why was it so important for him that the people cry?
The Yad Yosef explains that the difference between a human and a Malach is that in Tanach humans are "Holchim" those who go, while Malachim are always referred to as "Omdim" those who stand. The human experience is one of achievement that leads to growth. Humans are challenged daily on their mission because only by conquering obstacles can one growth. A person cannot stay still in the world he must constantly be on the go, climbing to greater heights each day.
Malachim are the ultimate dependable emissary of Hashem. They perform their mission but face no obstacles. Malachim by definition cannot grow. Malachim are always standing in one place.
After death a person leaves this world and can no longer grow on his own. The only way he can move up in the eternal world is through the mitzvos he inspires in the people he left behind in this world. Rav implored Rav Shmuel that after his death to please inspire the people to follow his good ways for "Hasam Ka'imna", over there he is standing and cannot grow.
The greatest gift we can give to a Niftar whether a relative, mentor, or friend is to emulate their ways and help them continue to grow even after leaving this world.