The Zohar teaches: “The tzaddik, even though he has departed from this world, is found in all worlds even more than during his lifetime.”
In other words, after the tzaddik’s passing, he is found in all worlds – including this world.
In the Tanya, this is explained straightforwardly:
The tzaddik’s life in this world is bound to the physical body, which limits the soul through the limitations of time and place and through the faculties and concepts of the body.
However, after his departure from this world, the tzaddik is in a different state – he belongs to the lofty heights of the soul, unbound by the limits of time and place and unconfined to the body.
This is another form of existence, of life in a world that is different and higher than the one with which we are familiar.
Hence, after his departure, the tzaddik can be in this world more than he was during his lifetime.
–Rabbi Adin Steinsaltz