What does this Mizmor discuss?
Rashi (111:1): It discusses the praise of a Tzadik.
Radak: It describes the Midos of a straight person whose reward is complete from Hashem in this world and the next.
How is this Mizmor according to the Aleph-Beis?
Refer to 111:1:2:1.
Why does it say "Ashrei ha'Ish"?
Avodah Zarah 19a: Happy is one who fears Hashem while he is still an Ish. Sha'arei Teshuvah (1:9) - i.e. the best Teshuvah is in one's youth, when he still has his strength, and he overpowers his Yetzer.
Malbim: The previous Mizmor ended with "Reishis Chachmah Yir'as Hashem." Such a person, Chachmah will come in his heart to guard the Torah's Chukim.
Who is considered "Yarei Es Hashem"?
Radak: He guards everything that Hashem commanded to do and to refrain from doing. He refrains from Mitzvos Lo Sa'aseh because fear of Hashem is on him, and not due to fear of people - covertly, just like openly.
Malbim: This is unlike one who is Yarei me'Hashem. Yarei Es Hashem implies fear of His exaltedness, not fear of punishment. The latter does not desire His Mitzvos, just he must do them from fear of punishment, or amidst hope for reward, but not amidst desire for the Mitzvah itself. The former desires the Mitzvah itself. Via fearing Hashem, he merits to understand the secrets and reasons for Mitzvos, and due to this he desires them greatly.
What do we learn from "b'Mitzvosav Chafetz Me'od"?
Radak: He does Mitzvas Aseh with his heart's desire and love of Hashem, and not to aggrandize himself in front of people or acquire a reputation. "Me'od" teaches that no desire or love enters his heart, only love of Hashem. He pursues Mitzvos and strives with all his strength to do them, with his body and money.
Radak citing Avodah Zarah 19a: He desires the Mitzvos, and not their reward. 'Do not serve Hashem like servants who serve for the sake of reward, rather, like servants who serve not for the sake of reward' (Avos 1:3).
Radak citing Shocher Tov: This refers to Avraham. Hashem told him "Lech Lecha me'Artzecha umi'Moladtecha", and immediately "va'Yikach Avram Es Sarai Ishto" (Bereishis 12:1, 5). Hashem told him "Himol", and immediately "b'Etzem ha'Yom ha'Zeh Nimol Avraham." "Kach Na Es Bincha Es Yechidecha", and immediately "va'Yashkem Avraham ba'Boker" (ibid., 17:10, 26, 22:2-3).
Malbim: Refer to 112:1:4:2.