Rambam on Meriting Eternal Life in the World to Come by Performing Mitzvot with Love

"It is a fundamental principle of the Torah that in order to merit eternal life in the World to Come a person must fulfill at least one mitzvah properly with complete devotion to God. This mitzvah must be performed without incorporating in it any personal interest in the observance, intending it only fulfill God will with love."

-- Rambam, Peirush HaMishnayot, Makkot 3:16

The Rambam is commenting on the following mishnah:

"Rabbi Chananaia ben of Akashya says: The Holy One, Blessed is He, wanted to confer merit upon Israel, therefore he gave them Torah and mitzvot in abundance. As it says, 'Hashem desired for the sake of Israel's righteousness, that the Torah be expanded and strengthened.' (Isaiah 42:21)." -- Mishnah, Makkot 3:16

One should clarify Rambam's conception: "... performed without incorporating in it any personal interest..." This would be negated should one be performing the mitzvah with the intention to "merit eternal life in the World to Come."
  

Sefer haChinukh on the World to Come not Mentioned in the Written Torah

"Should one ask further: After you have said that the primary aspect of all Creation is the world of souls (olam ha-neshamot) and that the ultimate reward for observance of the mitzvot is received there, why does God not mention it in the Written Torah and say explicitly, 'When you perform My mitzvot, I will bequeath you a share in the World to Come'?

"The answer is as follows: It is because the idea of the World to Come is known and obvious to all who possess intelligence; it is as clear as the sun. There is no nation or culture that does not agree that souls endure after the bodies have ceased to be; nor is there anyone who disputes that commensurate with the goodness of a soul, its wisdom, and the righteousness of its deeds, its pleasures in that world is correspondingly greater.

"This is logical, for the origin of the intelligent soul is the Source of Intelligence, i.e. God, and the closer the soul draws to its natural environment, to the place from which it originates, the greater is its pleasure."

-- Sefer haChinukh, Introduction

While the anonymous author of the Chinukh was well versed in the thought of Maimonides, who was thoroughly of Aristotelian persuasion, this passage is very similar to Platonist doctrines on the soul, such as found in Phaedrus, Philebus, etc.