Mishna: The greatest zechusim for neshamos

Our sages tell us that all of this world is an anteroom to the World to Come, and the reward for our actions in this world will come to us in the next world. It’s very possible that we will only realize how great the reward for our actions, good deeds, and Torah learning is once we reach the Next World.

However, once a Jew passes onto the Next World, they can no longer add meritorious actions to their accrued merits. This can be a source of particular anguish to those who suddenly realize how valuable good deeds and Torah learning are, and therefore they want more such merits. Our sages tell us that friends and family have the power to contribute mitzvos and Torah study for the benefit of departed souls, so that they may reap Divine rewards.

The ultimate form of contributory learning is through studying Mishnayos. While even a small portion makes a difference, the accepted custom is to complete all 63 tractates of the Shishah Sidrei Mishnah, first in time for the shloshim, and then annually in time for the yahrtzeit.