R. Yonah #1: The previous verse said "Rav Adam Yikra Ish Chasdo." Such a man does not go in the Derech of perfection and Temimus in Mitzvos. Therefore, it says that a Tzadik goes in his perfection and innocence. He does Mitzvos like they should be done, to fear Hashem and love Him, and not for grandeur and glory. One is a Tzadik only if he goes purely in Avodas ha'Borei.

R. Yonah #2: A Tzadik is one who is careful to avoid sin, and his deeds are proper. After he strives to perfect the Midos of his Nefesh, and he expels from his heart envy, desire and loce of honor, and he reaches the level of fear and Bitachon, he is called Tamim. "Ish Tzadik Tamim Hayah" (Bereishis 6:9). After the level of Tzadik, the level of Temimus is higher. This verse informs that even if a Tzadik did not reach the level of Temimus, but he goes purely in his ways, his Mitzvos are on the path of Temimus. Mis'halech refers to the actions, like "Holech b'Yashro Yerei Hashem" (14:2).

R. Yonah #3: Even if he did not reach the level of Temimus, he habituates his Nefesh to the Midah of Temimus, therefore he does not aggrandize himself for his Chasadim and deeds of Tzedakah.

Malbim: Tzadik is one who does deeds of Tzedek, but he is not yet Tamim. Temimus is doing everything only l'Shem Hashem, and not for honor, glory or other motivations. Then, he will not always stand in his virtue. This is connected to "Ish Emunim Mi Yimtza" (6). If so, also the Tzadik is not Tamim to do in Emunah.

R. Yonah: He brings merit to his seed after him. Those who do Mitzvos for grandeur and glory, even though they receive what is proper for them, they are not among Tzadikim with whom a Bris is made for them and their seed - "b'Yir'as Hashem Mivtach Oz ul'Vanav Yihyeh Machseh" (14:26). One who fears Hashem merits for his sons. "v'Oseh Chesed la'Alafim l'Ohavai" (Shemos 20:6) - for those who do amidst love, "ul'Shomerei Mitzvosav l'Elef Dor" (Devarim 7:9) - for those who do amidst fear (Sotah 31a).

Malbim: However, a Tzadik who goes purely in his ways to do everything l'Shem Shamayim ¹ , even though he does not get the imaginary praise, his children after him are fortunate, for the reward of Temimus remains for his children for all generations.

Ru'ach Chayim (Avos 5:3): Midos that a Tzadik toiled to attain, for his children they are like innate nature; with small exertion, they will attain them. Michtav me'Eliyahu (1, p.10) - one who did not toil to attain the level of his fathers, he has no Zechus Avos.