The Machlokes is in Hilchos Teshuvah 8:4.

The dispute is whether, after death, the Neshamah can attain new heights. The Rambam holds that the Neshamah does not develop after the person's Petirah, while the Ra'avad argues that if so, that this is the "Se'udah" that Chazal talked about, then there is no cup of blessing, because "blessing" means flourishing, while according to the Rambam it is all static.

The Rogatchover writes that the Machlokes between the Rambam and the Ra'avad is the same as the Machlokes in Kesuvos 39a concerning whether there is "Beger" ("maturation") in the grave or not. The Rambam maintains that one does not "mature" in the grave, while the Ra'avad mantains that one can.

Kol Tuv,

Dovid Bloom

Sam, it seems to me that according to the Rambam the chief factor determining where the Neshamah is in Olam ha'Ba depends on the Mitzvos that it did in this world.

1) See the Maharsha to Sanhedrin 104a, DH Aba, where the Gemara states that "Bra Mezakeh Aba." The Maharsha writes that there are some people who -- while they themselves are Resha'im -- do not want their children to grow up to be like them, but want them to be Tzadikim. Sometimes such parents educate their children to go on the good way and reproach their children when they see them doing wrong things. According to the Maharsha, "Bra Mezakeh Aba" means a Zechus that a person gains from what he achieved before he died.

2) Rav Shlomo Kluger zt'l also appears to learn that "Bra Mezakeh Aba" means that the main Zechus in the next world is something which is decided in a person's lifetime, not after he dies. In Ha'Elef Lecha Shlomo, Orach Chaim #61, he writes that the reason why the "son is Mezakeh the father" is simply that the father brought a good son into this world. ,Therefore even without doing anything else apart from physically bringing a Tzadik into the world, the father still possesses a Zechus. Again, according to Rav Kluger, it depends on what happened before the father died, namely that he caused a good son to enter this world.

3) Another source to support what the Rogatchover writes about the Rambam's opinion on the Neshamah after the Petirah, that "it does not attain new achievements, but is considered as 'standing still,' similar to Mal'achim" is as follows.

As far as I know, the Rambam never mentions the idea of "Kadish Yasom," the Kadish that an orphan says for his parents. At the end of Sefer Ahavah, the Rambam presents "The Order of Tefilos of the Entire Year." One of the sections is entitled, "the Nusach of the Kadish." If one looks carefully, one notices that the Rambam does not mention Kadish recited by a mourner or orphan. He mentions a few times the Kadish recited by the Shali'ach Tzibur, and he also mentions Kadish d'Rabanan recited after learning Torah, but he makes no mention of Kadish Yasom.

The Rambam also mentions Kadish in other places, such as Hilchos Tefilah 9:13 and 12:20, but again this refers only to the Kadish said by the Shali'ach Tzibur with no mention of Kadish Yasom.

Also, in a Sefer on the ancient customs in Yemen entitled, "Orach la'Tzadik," page 226, the author (Rav Tzovri) writes that the Kadish of "Yehei Shelama" does not exist in the ancient Yemenite Nusach. As is well-known, the Yemenite customs are often based on the rulings of the Rambam, so this is a support for the Rogatchover's notion that, according to the Rambam, the Neshamah does not attain new achievements after its departure from the body. We therefore can understand why the Rambam does not mention a Kadish said for the Niftar.

Kol Tuv,

Dovid Bloom